| Written by Mark Buzinkay
How is a warehouse organized?
Warehouses are typically expansive spaces supported by a grid of columns. Placing grid location labels on all sides of these columns makes communication with forklift drivers significantly more efficient. A widely used, effective, and easily understood approach for identifying specific locations within pallet racks relies on four coordinates that correspond to the aisle, rack, level, and bin:
- Aisle: This refers to the walkway situated between two shelving racks. Each aisle can be designated with a single identification number that applies to both the left and right racks or with two separate identifiers—one assigned to the rack on the left and the other to the rack on the right.
- Rack: A rack is a structural system designed for storing materials in horizontal rows, often incorporating multiple vertical levels to maximize storage capacity.
- Bay (also referred to as a rack unit): A bay represents the fundamental storage unit within a rack. It is defined as the space located between two vertical rack columns.
- Levels: Levels are the vertically stacked storage areas within a rack, allowing for the organization of materials at different heights.
- Bin: A bin is a specific, clearly defined storage location containing one or more compartments or slots for various products. Each bin is typically marked with a location identifier, such as a barcode, making it the most precise indicator of a warehouse storage location.
Simply labelling a shelf with a slot identification is not always enough to guarantee that the designated items will stay properly aligned with their assigned locations. While there is minimal risk of pallets becoming misaligned within a rack section designed to hold three pallets, misalignment can easily occur on open shelves where small bags or bins containing various items are stored. This issue can be effectively mitigated by using physical dividers or separators to create distinct, materialized slots that help maintain proper organization. In certain setups, additional aids like the pick by light system can further enhance accuracy in picking and placement processes.
Manual storage and retrieval systems
Storage and retrieval systems come in many different forms and operational methods. Customizing these systems to meet specific needs can result in a more cost-effective solution that performs better than a generic, one-size-fits-all approach. However, the actual performance of any system depends heavily on how effectively it is utilized and managed.
Narrow aisles and mobile racks are modifications of single-deep pallet racks designed to achieve higher storage density, though they require specialized equipment. The cost of investing in equipment for narrow aisles may be easier to justify if it enables operators to ride up to higher levels and pick individual boxes directly from pallets. Similarly, double-deep, drive-in, and pushback racks are designed to increase storage density. These systems also require special equipment and store items in multiple pallet units using a last-in-first-out (LIFO) retrieval method.
Compared to single-deep racks, these systems typically require less labour for storage and retrieval tasks. Flow racks are intended for items with dedicated storage locations, supporting first-in-first-out (FIFO) retrieval at the pallet level, and demand the least amount of labour among the methods described. On the other hand, block-stacking involves stacking pallets directly on top of each other without the use of racking infrastructure.
Block stacking is one of the few storage methods commonly used in manufacturing environments besides single-deep racks and flow racks. Its primary advantage is that it requires no investment in racking systems and relies on the same forklifts already in use within the facility for other operations. Since it does not involve racking, block stacking depends on stackable pallets, meaning the container walls must be strong enough to support the weight of multiple vertically stacked pallets. From a labour perspective, block stacking is the complete opposite of flow racks. While flow racks rely on gravity to move pallets, block stacking is highly labour-intensive because no items move unless a forklift physically relocates them.
By design, block-stacking typically operates as a last-in-first-out (LIFO) system. However, with careful arrangement, stacks of pallets can be organized into first-in-first-out (FIFO) lanes, similar to cars lining up in multiple queues to board a ferry. In this setup, each lane is dedicated to a single item, which limits the variety of items that can be stored compared to racking systems that allow different products to be stored at various levels within the same floor space. These characteristics make block stacking well-suited for high-volume, low-mix operations, where the truckload ships out items daily. Due to its low initial setup costs, block stacking is often the preferred storage method when a manufacturing plant is just starting operations, even if it may not meet the plant's long-term storage and efficiency requirements.
Automated Storage and Retrieval Systems (AS/RS)
None of the storage methods discussed earlier involve automation. While all movements are power-assisted, human operators carry out every action manually. In contrast, Automated Storage and Retrieval Systems (AS/RS) significantly reduce the need for direct human involvement. In such systems, the operator's role is limited to either (1) placing materials into a loading station and recording the loading transaction within the control system or (2) requesting materials through the control system and unloading them upon delivery. The process of selecting a storage slot and the physical movements of materials to and from that slot are fully automated, occurring without human intervention and at a faster pace than manual systems.
AS/RS can become economically viable in environments where extremely high volumes of materials are handled, where maximizing storage density is essential due to space limitations, and where maintaining precise inventory accuracy is critical. The key advantages of using an AS/RS include reduced labour required for moving items into and out of storage, improved accuracy in inventory tracking, and more efficient use of available space, leading to space savings.
Despite these benefits, AS/RS systems, much like Automated Guided Vehicles (AGVs), have been around since at least the 1980s, yet they are not widely adopted in manufacturing warehouses. Even in facilities where they are installed, it is not uncommon for users to express dissatisfaction with their investment. However, there is an important distinction between the decision to acquire an AS/RS when a facility does not already have one and the decision to remove or decommission an AS/RS that has already been purchased, installed, and integrated into operations.
What AS/RS systems exist these days?
Carousels
Carousels are simpler and more cost-effective Automated Storage and Retrieval Systems (AS/RS), primarily because they operate along a single axis of movement. Among these, the vertical carousel is a more complex machine but has the advantage of utilizing less floor space. The movement of a carousel can either be manually controlled by an operator or managed by an automated control system that tracks the specific storage locations of items within the carousel.
A vertical carousel (also known as a paternoster) operates on a continuous loop, cyclically bringing all storage locations to the operator's workstation. However, modern systems often replace this design with storage lifts, capable of retrieving and delivering only the specific part needed directly to the operator. A storage lift functions as an AS/RS designed specifically for handling small parts, offering improved efficiency over traditional vertical carousels.
In most manufacturing environments, the case for implementing carousels is not particularly strong. The main disadvantage lies in their sequential access mechanism, which can be a significant limitation. To retrieve a desired item, the system may need to cycle through multiple other items, resulting in wait times for the operator that is comparable to the time it would take to retrieve the item using traditional methods manually.
AutoStore, Robotics, and Forked AGVs
AutoStore is a large-scale AS/RS system designed with a cubic layout, where robots are responsible for placing items into storage and retrieving them from the top of densely packed racks. This system is widely utilized in retail warehouses due to its efficiency in handling high inventory volumes. In manufacturing environments, AutoStore can be particularly valuable for managing high-value products where accuracy, security, and space optimization are critical, especially in facilities where space is extremely limited or comes at a premium cost.
Amazon Robotics employs a different approach, where small mobile Automated Guided Vehicles (AGVs) are used to move entire racks directly to human pickers. This system is implemented in numerous Amazon fulfilment centres, enabling faster and more efficient picking processes in large-scale operations.
Forked AGVs, on the other hand, are automated forklifts that leverage advanced vision systems and navigation technologies to drive and operate independently without human intervention. These AGVs are capable of performing complex material handling tasks, including lifting, transporting, and placing pallets within warehouse environments.
Due to the high capital investment required for these advanced systems, their adoption tends to be more prevalent in large distribution centres operated by major retailers rather than in typical manufacturing facilities. Their cost-effectiveness and efficiency become more justifiable in environments with extensive inventory management needs and high throughput demands.
Pick 2 light systems
Pick 2 light guides manual picking by illuminating the bins that contain the required items. This system comes in numerous variations and is widely used in many factories, where it helps reduce training time, decreases picking errors, and boosts picker productivity. Pick 2 light is considered a form of usability engineering. It is not classified as automation or Jidoka because its role is limited to providing prompts to the operator without performing the task. Additionally, it is not a form of mistake-proofing since it does not physically prevent errors from occurring. Instead, it serves as an intermediate technology—a transitional tool that bridges the gap between manual processes and full picking automation. At the same time, it can be seen as an example of how technology can be applied to make work easier for people rather than to completely automate tasks.
With pick 2 light, pickers are no longer required to search for the correct bins, containers, or bobbins, simplifying the picking process. Additionally, Materials Managers can change bin locations as needed without confusing the pickers. Since the system supports manual picking rather than replacing it entirely, it is best described as a form of semi-automation. At just a fraction of the cost of fully automated picking systems, pick 2 light offers clear, tangible benefits, making it a popular choice in warehouses and manufacturing facilities (as an alternative, see also: RFID tracking).
Manufacturers primarily use pick 2 light for kitting in supermarket areas and lineside picking at assembly stations. On factory shop floors, 'supermarkets' refer to small, organized storage areas located near assembly operations and managed by the production team. The materials organization is responsible for replenishing the racks from external inventory sources. Dedicated production operators then pick kits from the supermarket and deliver the parts directly to the assembly lines for immediate use. Assembly teams have found that pick 2 light significantly improves picking accuracy and speed. In some cases, to eliminate the need for a separate kitting step, pick-to-light systems are installed directly on lineside shelves, allowing operators to pick parts and assemble them simultaneously.
While guiding pickers by lighting up the correct bins is relatively straightforward, verifying that the correct items and quantities are picked—and ensuring that this information is reported accurately to Production Control—is a more complex challenge. Asset Agent is one example of a system designed to handle picking guidance and validation.
Certain pick 2 light systems display the required pick quantity directly on the bin and include a button for the operator to press once the pick is complete. Other systems employ light curtains positioned in front of each bin. In these setups, the picker's hand movement breaks the light curtain when reaching into the bin and restores it upon withdrawal, signalling to the system that the pick is finished. However, this method still does not verify the accuracy of the picked quantity.
Asset Agent enhances the process by identifying the correct bin and communicating directly with the receiving machine to confirm whether the correct bin has been selected. It provides immediate visual feedback by signalling a match or mismatch with a light, adding an extra layer of validation to the picking process.
The global market for Pick to Light was estimated at US$506.1 Million in 2023, and is projected to reach US$789.5 Million by 2030, growing at a CAGR of 6.6% from 2023 to 2030. (2)
FAQ: Pick 2 Light Systems
What is a pick 2 light system and how does it work?
Pick 2 light is a semi-automated system that guides manual picking by illuminating bins containing the required items. Lights are activated based on picking instructions, helping operators quickly identify the correct bins. Once the item is picked, the operator can confirm the action by pressing a button or triggering a sensor, ensuring accuracy and reducing the chance of errors.
What are the benefits of using pick 2 light in warehouse operations?
Pick 2 light systems improve picking accuracy, reduce training time for new employees, and increase productivity by minimizing search time. They also offer flexibility, allowing Materials Managers to change bin locations without confusing operators. The system is cost-effective compared to full automation, making it ideal for warehouses and manufacturing environments.
How does pick 2 light differ from full automation systems?
Unlike fully automated systems, pick 2 light supports manual picking rather than replacing human labour. It guides operators visually but relies on them to perform the actual picking tasks. This makes it a form of semi-automation, offering efficiency gains without the high costs and complexity associated with fully automated storage and retrieval systems.
Takeaway
Pick 2 light solutions offer a cost-effective way to enhance manual picking efficiency, reducing errors and training time while improving productivity. As a form of semi-automation, it supports operators without replacing them, making it ideal for kitting and lineside assembly tasks. For operations seeking greater accuracy and validation, technologies like Asset Agent add an extra layer of control by verifying picks in real time and communicating directly with receiving systems. Together, pick 2 light and Asset Agent represent a practical evolution toward smarter, more efficient warehouse management without the complexity or cost of full automation.
Delve deeper into one of our core topics: Real time location systems
Glossary
Automated Guided Vehicles (AGVs) are mobile robots used in industrial settings to transport materials without human intervention. They follow predefined paths using guidance technologies like magnetic strips, lasers, or vision systems. AGVs improve efficiency, reduce labour costs, and enhance safety in warehouses, manufacturing plants, and distribution centres. They are commonly used for repetitive tasks such as pallet handling, towing, and inventory transport. (3)
Sources:
(1) Baudin M., Netland T. (2023): Introduction to Manufacturing. New York: Routledge
(2) https://www.globenewswire.com/news-release/2024/08/23/2934754/28124/en/Pick-to-Light-Market-Forecast-Report-2024-2030-Adoption-of-Pick-to-Light-in-Cold-Storage-and-Food-Industry-Expands-Addressable-Market.html
(3) Bostelman, R., & Marvel, J. (2019). Performance Measurement of Industrial Mobile Robots and AGVs. Springer
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