Horizontal Carousels in Logistics

Horizontal carousels are advanced storage and retrieval systems designed to improve warehouse efficiency and productivity.

Updated 2026-02-20

Overview

Horizontal carousels are advanced automated storage and retrieval systems (AS/RS) designed to optimize the retrieval and storage of goods in a warehouse environment. These systems consist of a series of bins or trays that rotate horizontally around an oval track, presenting items to an operator at a designated pick station. This "goods-to-person" principle allows for quick access to inventory without the need for manual searching or extensive travel by the picker. The primary purpose of horizontal carousels is to significantly increase warehouse efficiency, reduce labor costs, and minimize the time spent locating and picking items, making them an essential asset in modern logistics operations, particularly for high-volume, small-item order fulfillment.

Etymology and Origins

The term "carousel" originates from the French word "carrousel," which refers to a rotating game or exhibition, often involving horse riders. The term itself is derived from the Italian "carosello," meaning a small battle or tilting match, and later evolved to describe a circular platform ride 5. In the logistical context, the concept of a rotating storage system began to be explored as industries sought more efficient ways to manage growing inventories.

The application of "carousel" to storage systems emerged in the mid-20th century, coinciding with the rise of mechanization in material handling. Early engineers and designers recognized the rotational mechanism's potential to bring stored items to a fixed operator, much like a fairground carousel brings riders past a central point. This innovation directly contrasted with traditional storage methods where operators walked to static shelves. The first iterations of these automated systems, both horizontal and vertical, were developed to cater specifically to the burgeoning needs for quick and efficient item retrieval in retail, manufacturing, and distribution sectors, particularly for handling large quantities of small components or diverse SKUs.

Historical Development

The evolution of horizontal carousels is deeply intertwined with the broader development of automated storage and retrieval systems (AS/RS) that gained prominence in the post-World War II industrial expansion. The increasing complexity of supply chains and the need for faster order fulfillment spurred innovations in material handling:

1950s - Early 1960s: The foundational concepts of mechanized storage began to take shape. Early AS/RS designs primarily focused on palletized loads using crane-based systems. However, the demand for efficient handling of smaller items for piece-picking operations led to the development of alternative solutions 6. The first horizontal carousel systems, often rudimentary in their automation, were introduced, applying mechanical and electrical components for automated item retrieval in environments like parts departments and tool cribs.
Late 1960s - 1970s: This period saw significant advancements in the design and adoption of horizontal carousels. Companies like Kardex Remstar (a prominent manufacturer of storage and retrieval systems) and Richards-Wilcox (with its early 'White' carousels) pioneered more robust and efficient designs. These systems improved the speed and integration of goods into existing warehouse layouts, primarily serving high-volume retail and manufacturing environments for storing small components, tools, or documents. The focus was on optimizing space utilization and reducing walking time.
1980s: The advent of affordable microcomputers and programmable logic controllers (PLCs) revolutionized carousel technology. This decade witnessed the incorporation of sophisticated control systems, moving beyond simple push-button operation to more intelligent management. These advancements allowed for better inventory control and management through early forms of warehouse management software (WMS), which could interface directly with the carousel's control system. This integration enabled features like optimized rotation sequences and basic inventory tracking.
1990s - 2000s: Further advancements in software and material handling equipment led to more efficient and reliable carousel operations. The rise of enterprise resource planning (ERP) systems and more powerful WMS platforms allowed for seamless integration of carousels into broader supply chain operations. Features such as light-directed picking (pick-to-light) and software-driven batching became standard, significantly increasing picking accuracy and throughput. The industry began to emphasize modularity and scalability to adapt to changing business needs.
2010s to Present: The digital age brought about a new wave of innovation. Continuous improvements in sensor technology, connectivity (IoT), and advanced analytics have resulted in highly intelligent carousel systems. Modern carousels offer enhanced efficiency, predictive maintenance capabilities, and tighter integration with visual inventory management systems and order management systems. The focus has shifted towards creating fully integrated, data-driven order fulfillment solutions, often combining carousels with other automation technologies like conveyors and robotics.

Core Concepts

Horizontal carousels operate on a simple yet highly effective principle known as "goods-to-person" picking: modular trays move around a circular or oval track, bringing items directly to the operator at an ergonomic workstation. This system significantly reduces the time and effort needed for picking items, eliminating picker travel time which can account for up to 60-70% of order picking costs in traditional warehouses 7. Some core features and advantages include:

Automated Retrieval and Sequencing: Systems are integrated with advanced inventory management software and WMS for real-time data on stock levels, order priorities, and retrieval schedules. The software sequences carousel rotations to present the required items in the most efficient order, often using pick-to-light or voice-picking technologies to guide the operator.
Space Efficiency (Cube Utilization): Carousels make optimal use of both vertical and horizontal space. By utilizing overhead space and minimizing aisle requirements, they allow for a significantly greater storage density compared to traditional shelving or static racks. This is particularly beneficial in facilities with high ceiling clearances or limited floor space.
Ergonomic Design and Operator Safety: By bringing items directly to the operator at a comfortable, stationary workstation, carousels eliminate the need for excessive walking, bending, reaching, and lifting. This not only minimizes worker fatigue and strain, but also reduces the risk of workplace injuries, leading to improved employee morale and productivity.
Security and Inventory Protection: Enclosed carousel systems can provide enhanced security for valuable or sensitive inventory, protecting it from dust, damage, and pilferage. Access can be restricted and tracked through the WMS, adding an extra layer of control.

Types and Classifications

Horizontal carousels can be configured in various ways to suit different operational needs and throughput requirements:

Single-Item Picking (Discrete Picking): Designed for high-velocity items where each retrieval is for a single SKU required by an individual order. The system quickly presents the correct bin to the operator, often guided by light-tree displays, to fulfill one order at a time. This method prioritizes speed and accuracy for specific, urgent orders.
Batch Picking: This configuration is highly efficient for fulfilling multiple orders simultaneously. Operators pick multiple units of an item to fulfill several orders from a single carousel presentation. The system uses a put wall or multiple order totes at the workstation to sort items into individual orders as they are picked, significantly optimizing the picking process and reducing carousel rotations per order. This approach is ideal for high-volume e-commerce fulfillment.
Zone Picking: In larger installations, multiple carousels can be arranged into distinct zones. Each zone is responsible for picking items only within its assigned carousel(s). Orders are passed from one zone to the next (e.g., via a conveyor) until all items for an order are collected. This parallel processing greatly increases overall system throughput.
Dynamic Carousels (Integrated Systems): These are advanced systems that can adjust speed and item retrieval based on real-time demand, integrating seamlessly with advanced inventory management systems and conveyors. They often work in conjunction with sophisticated WMS algorithms that analyze order profiles and optimize carousel rotations, batching strategies, and even predict future picking needs. Some dynamic systems can also be linked with robotics for fully automated retrieval and placement.

Industry Applications

Horizontal carousels are versatile and utilized across various sectors where efficient handling of small to medium-sized items is critical:

E-commerce Fulfillment: Central to accelerating order processing and improving delivery times. Carousels enable rapid, accurate picking of diverse SKUs for individual customer orders, helping e-commerce companies meet demanding service level agreements.
Pharmaceuticals and Healthcare: Highly regulated environments benefit from the precision, accuracy, and security of carousels. They are used for storing and retrieving medications, medical devices, and supplies, ensuring strict inventory control, tracking expiration dates, and preventing errors crucial for patient safety and regulatory compliance.
Manufacturing and Assembly: Streamlining parts storage and retrieval for just-in-time (JIT) production processes. Carousels ensure that assembly line workers have immediate access to components, minimizing line stoppages and improving manufacturing efficiency, especially for products with a high number of small parts.
Retail Back-of-Store/Distribution: Used for replenishing store shelves, managing returns, or fulfilling click-and-collect orders. They optimize the flow of goods from receiving to dispatch, ensuring product availability and efficient space utilization.
Automotive: Ideal for managing spare parts inventory, tools, and maintenance supplies in dealerships, service centers, and manufacturing plants, ensuring quick access for repairs and production.
Tool Cribs and MRO (Maintenance, Repair, and Operations): Provides secure, organized storage and efficient retrieval of tools, spare parts, and consumables, reducing search time and inventory loss in industrial settings.

Benefits and Advantages

The integration of horizontal carousels in logistics and order fulfillment offers numerous compelling benefits:

Increased Throughput and Efficiency: By bringing items to the operator, carousels drastically reduce walking time and search time, which are major bottlenecks in manual picking. This can lead to a 2-4x increase in picking speed and overall throughput compared to traditional methods 8.
Lower Labor Costs: Automation significantly decreases the reliance on manual labor for non-value-added tasks like walking and searching. This allows existing staff to handle a higher volume of orders, reducing the need for additional hires or enabling reallocation to more complex tasks.
Improved Inventory Accuracy: Real-time tracking and integration with WMS minimize human error during picking and putaway, leading to superior inventory accuracy and reduced discrepancies. This helps prevent stockouts, overstocking, and ensures reliable order fulfillment.
Optimized Space Utilization: Horizontal carousels achieve high-density storage by using available vertical space and minimizing aisle requirements. This can reclaim up to 60-70% of floor space compared to static shelving, allowing for higher storage capacity within the same footprint or reducing overall facility size 9.
Enhanced Ergonomics and Safety: The "goods-to-person" principle eliminates walking, bending, and reaching into shelving, creating a safer and more comfortable working environment. This reduces physical strain, prevents injuries, and improves operator morale and productivity.
Scalability and Flexibility: Modern carousels are often modular, allowing for future expansion by adding more units. They can also be reconfigured or integrated with other automated systems to adapt to changing order profiles and business growth.

Challenges and Limitations

While horizontal carousels offer various benefits, potential challenges and limitations must be considered during their implementation and operation:

High Initial Cost and ROI: The upfront investment for purchasing, installing, and integrating horizontal carousel systems can be significant, particularly for smaller operations. A thorough Return on Investment (ROI) analysis is crucial to ensure the long-term benefits outweigh the initial capital expenditure.
Maintenance Needs and Downtime: These complex electro-mechanical systems require regular, specialized maintenance to ensure optimal operation and longevity. Any mechanical or software failure can lead to significant downtime, impacting order fulfillment and requiring dedicated maintenance personnel or service contracts.
Integration Hurdles: Adapting existing WMS or ERP systems to new carousel systems may require substantial investment in software development, customization, and configuration. Seamless data exchange is vital for efficient operation, and poor integration can negate many of the system's benefits.
Throughput Limitations for Very High-Velocity Items: While efficient for small items, for extremely high-volume SKUs that move constantly, other AS/RS solutions like high-speed conveyors or shuttle systems might offer even greater throughput. Carousels are best suited for medium to high-velocity items, not typically for full-case or pallet-level picking.
Inflexibility in Layout Changes: Once installed, the fixed track layout of a horizontal carousel can be challenging and costly to reconfigure if warehouse operations or product types dramatically change. Planning for future growth and flexibility is essential during the initial design phase.
Dependency on Single Point of Failure: In a multi-carousel system, if one unit experiences a major breakdown, it can disrupt the entire picking process for the products stored within that unit, potentially affecting overall throughput.

Best Practices

To maximize the effectiveness and ROI of horizontal carousels, logistics professionals should adhere to these best practices:

Thorough System Design and Analysis: Before implementation, conduct a detailed analysis of inventory profiles (SKU count, velocity, size, weight), order profiles, and desired throughput. Choose the right number and type of carousels, and integrate them optimally within the overall warehouse layout.
Seamless WMS Integration: Ensure tight integration with a robust warehouse management system that can optimize carousel rotation sequences, manage inventory levels, track picks, and support advanced picking methodologies like batch and zone picking. This is critical for maximizing efficiency and accuracy.
Regular Training and Certification: Ensure all staff involved in operating, maintaining, and supervising carousel systems are thoroughly trained and potentially certified. Proper training reduces errors, improves safety, and empowers operators to troubleshoot minor issues.
Proactive Maintenance Program: Implement a comprehensive preventative maintenance schedule. Regular checks, lubrication, and calibration of mechanical and electrical components are crucial to prevent breakdowns, minimize downtime, and extend the lifespan of the equipment.
Inventory Optimization and Slotting: Continuously optimize inventory slotting within the carousels. Place high-velocity items in easily accessible locations and utilize software to re-slot based on changing demand patterns. Combine with effective stock replenishment strategies.
Performance Monitoring and KPIs: Establish Key Performance Indicators (KPIs) such as picks per hour, order accuracy rates, and downtime. Continuously monitor these metrics to identify areas for improvement and ensure the system is meeting performance targets. Productivity tracking features in WMS can be very helpful here.

Future Trends

As technology continues to advance, the future of horizontal carousels is likely to see further integration and intelligence:

Enhanced Integration with AI and Machine Learning: Expect more sophisticated predictive analytics for inventory management, demand forecasting, and optimized picking routes. AI algorithms will learn from historical data to dynamically adjust carousel operations, batching strategies, and even predict potential equipment failures for proactive maintenance.
Advanced Smart Systems and IoT: Expanding use of IoT sensors will enable real-time monitoring of carousel operations, component wear, and environmental conditions. This data will feed into predictive maintenance systems, reducing downtime and optimizing energy consumption. Smart systems will become more autonomous, capable of self-diagnosis and even self-correction in some scenarios.
Robotic Integration: Hybrid systems combining horizontal carousels with robotic picking arms or Automated Guided Vehicles (AGVs) and Autonomous Mobile Robots (AMRs) will become more common. Robots can perform the actual item picking from the presented carousel tray, further automating the goods-to-person process and extending operational hours without human intervention.
Increased Modularity and Scalability: Future designs will likely emphasize greater modularity, allowing businesses to easily scale their carousel systems up or down based on fluctuating demand without extensive rehauling.
Energy Efficiency and Sustainability: Continuous innovation will focus on developing more energy-efficient motors, control systems, and regenerative braking technologies to reduce the environmental footprint and operational costs of these systems.

Related Concepts

Horizontal carousels are closely related to other automated storage and retrieval systems (AS/RS) and material handling equipment, forming an integral part of modern warehouse automation strategies. Understanding their place in the broader spectrum of warehouse operations is essential for logistics professionals aiming to streamline and enhance efficiency in supply chains:

Vertical Carousels: Similar in principle but rotate vertically, making them ideal for high-density storage of smaller items in facilities with limited floor space but high ceilings.
Vertical Lift Modules (VLMs): Enclosed automated units consisting of two columns of trays and an extractor that moves vertically to retrieve and deliver trays to an access opening, offering highly dense storage.
AS/RS Cranes (Mini-load, Unit-load): Larger, crane-based systems designed for automated storage and retrieval of totes, cartons, or pallets in high-bay warehouses.
Conveyor Systems: Often integrated with carousels to transport items, totes, or completed orders between different zones or to packing stations.
Automated Guided Vehicles (AGVs) and Autonomous Mobile Robots (AMRs): Can be used to transport materials to and from carousel pick stations, further automating the internal logistics flow.
Pick-to-Light and Put-to-Light Systems: Technologies often integrated with carousels to guide operators to the correct pick location and quantity, significantly improving accuracy and speed.

Conclusion

Horizontal carousels have evolved from simple mechanical devices into sophisticated, software-driven solutions that are fundamental to modern, efficient logistics. By embracing these automated systems, businesses can achieve significant gains in throughput, accuracy, space utilization, and labor efficiency, positioning themselves for success in an increasingly demanding supply chain landscape.