Pros and cons of different warehouse automation and robotics solutions for order fulfillment

How to choose the right warehouse automation solution for order picking and fulfillment

Warehouses need an accurate and efficient fulfillment system to deliver exceptional customer service, remain competitive and operate profitably. To achieve this, warehouses must overcome two industry-wide challenges: chronic labor shortages and high error rates.

Finding and retaining qualified labor has been the #1 challenge for warehouses since 2017 due to persistent labor shortages and annual employee turnover of 49%. In addition, over 60% of retailers identify manual processes and human errors as the number one root cause for inventory and fulfillment issues, with error rates averaging 1-3%.

To combat these issues and reduce costs, companies are increasingly introducing automated fulfillment systems into their warehouses. Automated warehouses benefit from higher efficiency, improved picking accuracy, reduced labor needs and lower costs.

There is no one-size-fits-all solution when it comes to warehouse automation. Automation systems encompass everything from legacy conveyors to modern technologies like mobile robots and robotic picking, and each system has its own pros and cons.

The Evolution of Warehouse Automation


Considered the oldest and most traditional form of warehouse automation, conveyors consist of long winding strips of belts & rollers fixed in place and spread across a facility. Conveyors are used to sort and transport goods from one place to another. Conveyors are easy to operate and can handle a wide range of SKUs; however, they require integration with other piece-picking technologies for order fulfillment, which adds complexity to the implementation process and operations. Conveyors are also highly rigid and cannot be easily moved or reconfigured if business needs change, putting them at risk of becoming fixed ‘monuments’ inside a warehouse. In addition, they also suffer from having a single point of failure, meaning if one part of the conveyor breaks down it can cause the entire system to stop.

Pros: easy to operate, handles wide range of SKUs, can be used for sorting

Cons: highly rigid, difficult to reconfigure or scale, expensive, single point of failure, large amount of spare parts needed to maintain

Shuttle System

In a shuttle system, fast-moving shuttles travel horizontally across storage racks, retrieve storage totes and deliver them to a lift, which then takes the totes down to a conveyor to be delivered to a human or robotic picking station.

Shuttle systems have been on the market for approximately 20 years and account for ~70% of the automated fulfillment systems installed to date. They can reach heights of up to 60 feet, which makes shuttle systems space-efficient for large warehouses with lots of vertical height. On the other hand, they are typically not suitable for smaller warehouses or micro fulfillment centers. Shuttle systems can achieve high-throughput, however to do this they require advanced software that calibrates each tote’s sequencing on the lift module.

The main drawback of shuttle systems is their cost, being one of the most expensive forms of automation. Additionally, shuttle systems have long implementation times (sometimes up to 3 years) and high maintenance costs. Similar to conveyors, shuttle systems are also highly rigid and inflexible and cannot be easily reconfigured once installed. The lift modules also act as a single point of failure that can cause the whole system to stop.

Warehouse automation companies providing shuttle systems include Dematic, Knapp, Vanderlande, TGW, Exotec, Schaefer and Daifuku.

Pros: well-known established solution, high throughput, high density in large warehouses

Cons: expensive, long implementation times (1-3 years), inflexible and difficult to reconfigure, requires advanced software, single point of failure, difficult to maintain, expensive spare parts inventory, not suitable for most smaller warehouses (e.g. back-of-store and MFCs) or mezzanines

Cubic Storage

Cubic storage, also known as cube automated storage and retrieval (Cube ASRS), consists of totes densely stacked on top of each other in a cube-like structure. Mini-robots travel on top of the structure, retrieve totes from inside the cube and deliver them to external human or robotic picking stations.

Cube-based storage is the densest form of warehouse storage available, however it can only reach a maximum height of 20 feet (three times lower than shuttle). Cube ASRS is simpler to implement and maintain than shuttle systems. It is also more modular and does not have a single point of failure. However, it still relies on a fixed rigid structure that cannot be easily reconfigured, with strict design requirements such as perfectly-level floors. Installation times for cube ASRS are typically 6-18 months.

Throughput of Cube ASRS systems is slowed down when robots need to ‘dig’ to retrieve a tote several layers deep. That is why Cube ASRS systems are efficient only in 90/10 or 80/20 Pareto distributions (i.e. where 20% of SKUs account for most of the volumes, which means most high-volume items can be stored closer to the top).

Cubic storage currently accounts for 11% of the fulfillment automation market. Warehouse automation companies providing Cube ASRS include Autostore and Ocado.

Pros: high storage density (for medium-height warehouses), high throughput for high-runners

Cons: expensive, difficult to reconfigure, strict implementation requirements, long installation times, low throughput for medium- and slow-runners

Autonomous Mobile Robots (AMRs)

Mobile robots for ecommerce fulfillment automation were commercialized in the late 2000s and first employed by Kiva Systems (acquired by Amazon in 2012). Compared to shuttle or cube ASRS, mobile robots are significantly cheaper and easier to implement, scale and maintain. As a result, they are often available through a Robots-as-a-Service (RaaS) sales model that enables companies to pay a monthly subscription fee or lease per robot instead of buying them outright. RaaS significantly lowered the upfront capital expenditure for automation, thereby reducing business risk for customers and lowering adoption barriers. AMRs currently account for 11% of the fulfillment automation market, which is forecast to double by 2030.

There are several types of AMR systems for warehouses and fulfillment centers:

(i) Goods-to-Person (G2P)

In Goods-to-Person systems, AMRs retrieve totes or racks of merchandise from storage and transport them to centralized picking stations where human operators pick items out to consolidate orders. After all the necessary items are picked out of the tote or rack, the robots return the remaining items back into storage. 

Such systems eliminate human walking by using robots to transport all the items. With Goods-to-Person systems, a company on average needs one human per 8-12 robots. However, Goods-to-Person systems still require human operators to pick. Moreover, robots need to constantly travel back and forth to retrieve and return items, which negatively affects throughput and cycle times.

Goods-to-Person systems can be flexible and adaptable, although they often require special shelving and separation from humans due to safety concerns. The racks can go up to 16 feet high, offering competitive storage density (especially when used in mezzanines).

Warehouse automation companies providing Goods-to-Person systems include Geek+, GreyOrange, Hai Robotics, Quicktron and Addverb Technologies.

Pros: increased pick rates & accuracy, flexible and adaptable, competitive density

Cons: requires special shelving and separation from humans, reliant on human pickers

(ii) Goods-to-Robot (G2R)

Goods-to-Robot systems work just like Goods-to-Person, except the human picker is replaced by a robotic picking arm in the picking stations. This reduces human picking needs to zero (assuming all items are robotically pickable). Recent advancements in machine vision and AI have broadened the range of robotically pickable items to include most ecommerce and grocery items.

There are few providers of Goods-to-Robot systems given the complex software and AI needed for robotic picking. It is likely that in the future, systems integrators will combine technology from AMR and robotic picking vendors to create Goods-to-Robot systems. Currently only Brightpick provides an integrated AMR-based Goods-to-Robot solution.

Pros: end-to-end fulfillment automation with integrated robotic picking, eliminates labor challenges, flexible and adaptable, competitive density

Cons: requires advanced software, G2P stations necessary if some SKUs are not robotically pickable

(iii) Pick-Assist

In pick-assist systems, humans remove items directly from the shelves and place them onto AMRs. The AMRs move around the warehouse from one pick location to the next and, once the order is fully consolidated, deliver it to the packing station. As a result, human pickers only need to concentrate on one warehouse zone (e.g. 1-2 aisles), which reduces foot travel and increases productivity.

The main disadvantage of pick-assist systems is that they still require humans to do the picking. Moreover, humans need to move around in between picks, which means lower pick rates per human compared to Goods-to-Person systems. Pick-assist systems typically require 1 human per 3-4 robots.

The main advantage of pick-assist AMRs is that they are easy to implement, requiring no changes to the warehouse since humans continue picking from shelves, as in manual operations.

Warehouse automation companies providing pick-assist AMRs include Locus Robotics, 6 River Systems, Fetch Robotics and Rapyuta Robotics.

Pros: flexible, easiest to implement, safely operates around humans, low cost

Cons: high labor requirements, low human pick rates, low storage density

(iv) Autonomous Mobile Picking Robots

Autonomous mobile picking robots are robots that autonomously move around the warehouse and robotically pick and consolidate items within the aisles. They can best be described as a “Robot-to-Goods” (R2G) solution. They are much like a human with a cart, moving around the warehouse and consolidating an order by picking items from shelves.

In contrast to Goods-to-Person systems, autonomous mobile picking robots pick inside the aisles and do not need to travel back and forth to centralized picking stations. They also do not need to wait for human pickers inside the aisles to do the pick. As such, autonomous mobile picking robots can achieve higher throughput per robot. Moreover, because the robots both transport and pick the items, such a solution requires zero human labor.

Autonomous mobile picking offers the greatest throughput with the least labor and fewest robots. There are numerous benefits to this, including:

  • Less congestion and higher peak throughput as there are fewer robots traveling around the warehouse at peak hours
  • Lower cost per pick as the same throughput can be achieved with fewer robots and labor
  • Faster deployment since fewer robots need to be deployed
  • Lower labor needs and improved work environment

The main limitation of autonomous mobile picking robots is the complexity that comes with robotically picking items from shelves. This includes strict criteria for placing items on shelves, high error rates and a highly-manual replenishment process. These limitations can be solved by storing goods in totes, instead of directly on the shelves, and using proven piece-picking technology to pick them.

Pros: offers the greatest throughput with the least labor and fewest robots, flexible and adaptable, easy to implement, lowest cost per pick, competitive density

Cons: requires advanced software, G2P stations necessary if some SKUs are not robotically pickable

In the world of warehouse automation there are many choices. Each type of automation has its pros and cons depending on your needs. If you’re interested in learning more about how efficient each automated fulfillment system is, you can download our White Paper here.

About Brightpick
Brightpick offers the world’s most efficient warehouse automation solution for ecommerce and grocery order fulfillment. The company’s end-to-end robotic solution autonomously picks, consolidates and dispatches orders in large, small and micro fulfillment centers. The Brightpick solution takes less than a month to deploy, enables warehouses to reduce their picking labor by 95%, and cuts costs for order fulfillment by half. Brightpick is part of Photoneo Brightpick Group, headquartered near Cincinnati, OH, which has more than 300 employees and 5000 technology installations across the US, Europe and Asia. Photoneo Brightpick Group’s customers include leading companies such as General Motors, Volkswagen and KUKA.