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Warehouse Design – Sorters (amended)

Updated: Oct 23, 2020

1. Introduction



Note: this document has been revised to include the Grey Orange Flexo Sortation robots / Geek Plus - see section 9.

In my previous Blogs we have discussed that due to factors such as ecommerce growth, increased labour costs and a reduction in the availability of labour, that there will be a growth in the application of automated solutions in warehouses. These solutions also help with social distancing requirements we currently need to adhere too. We will continue to see significant increases with picking performance from systems with Goods To Man automation, including systems with Robots and Cobots. As the picking operations become more efficient it is logical that we will continue to see increased take up of automated packing solutions coupled with automated sortation solutions.


In this Blog I try to focus on the factors you need to consider when specifying and selecting a sorter. There are so many different sorter types available, I have summarised what I consider to be the most popular types of sorters applied to warehouse operations. Hopefully, you will learn something new about this fascinating area of automation. As an independent consultant and I have no bias to any supplier or any solution, and I aim to review the equipment in a subjective and objective way.


2. What tasks do Sorters actually perform?


In simple terms “sorters route items to a destination usually by means of a conveyor, at the appropriate transfer point the items are pushed or dropped the next part of the process”.

Although the basic concept at first glance could be considered as relatively simple, there are so many different sorters, and the design options are numerous. There are many different sorter types suited to different applications. The sorters can have numerous different types of divert mechanisms, including pivot arms, pop-up wheels, rollers, tilt trays, and pushers.

The final design would need to consider factors including the product shapes, sizes, and weights. The conveyor speed and the required throughputs will also need to be considered.

Sortation systems require a high level of capital investment, the payback period is likely to be many years. Any solution and operational design will need to consider any future volume growth forecasts.

What are the main benefits of a sorter?


Improved accuracy and productivity– reducing the need for manual handling and introducing automation, and reducing the possibility of human error, will no doubt increase the accuracy of an operation.

When compared to a manual sort operation, which is a comparatively slow process, typically involving scanning bar code labels and pushing cartons along a belt to either destination lane, or to another operator to repeat the process. The balancing of the workload between operators in a sorting area is difficult, and the work is mundane and can result in high occurrences of error.


Note: I have witnessed an operation where numerous cartons were continually being misrouted, in some cases customer orders were routed to Edinburgh instead of Plymouth. This resulted in the following sequence of events:

  • the original orders having to be returned through the network to the source location and the items being returned to stock,

  • a repeat order of the original order being picked, packed, and shipped

  • customer services having to contact a very dissatisfied customer.


Reduced costs – as the operation will become highly efficient there will no doubt be a reduction in operating costs, as with any major investment in automation you will need to calculate the ROI (Return on Investment) / Payback period of the sorter system as part of the financial justification.


Improved customer satisfaction – installing an appropriate sorter will ensure that the customers receive the correct goods, delivered on time with almost zero errors. Customers are very fickle and not providing excellent customer service is no longer acceptable.


How do we start the design process: what should we consider?


1. Product – what are you sorting, are the items in corrugated boxes, totes, trays, bags, sacks? Are the packs and contents fragile, are they suitable for conveying and sortation? What is the maximum, minimum and average length, width, height, and weight of items you are wanting to sort?


2. Rate – how many items do you need to sort per minute, per hour, per shift? What inefficiencies need to be considered such as breaks, shift changes, order release waves, truck / container arrival and departure times, etc.?


3. Number of diverts – how many sort destinations are required? Will the sorter need to sort to one or two sides? Where in the facility will the sorter be located, how much clear height is there? Do you need to sort by postal area, or by sortation hub, or by customer, or by store? Can the sort lanes be changed from one customer whilst the sorter is operating?


Sortation Systems Components:


A sorter system has 6 key components described below:

Typical Sortation Systems



1. Merges and conveyors: To facilitate a steady flow of goods by a continuous flow of items and funnelling of items before moving to the next stage the induction area.


Sorter Merge Sub System


Three into One Merge Sub System


2. Induction sub-systems: Minimise gaps between items and maximise the flow of goods onto the sorter, the size of the items will be considered as part of the induct process.

Induct Sub System


3. The sorter: the type of sorter, the type of divert options will need to be considered in accordance with the desired throughput requirements


4. Chutes: to consolidate the order and/or accumulate the items per destination


Sorter chutes – sacks – option 1


Chutes - designs may include gravity or rollers – heavy items may be sorted with light items, so the design of the chute is key to minimising damage. The drop angle, and the materials used on the chutes will need careful consideration, especially on longer shuts with products which are both heavy and light. Smooth surfaces (such as stainless steel), will result in items travelling at speed and possibly causing damage, abrasive surfaces could result in items not reaching the end point and causing obstructions to the system, possibly result in excessive items either recirculating or being sent to the dump lane.

5. Take-away conveyors: move goods away from the sorter to other areas of the system, this could include directly routing items to a boom conveyor to load despatch vehicles.


6. Controls System

As with any automated application in the background there is a control system. This system directs the items to the designated destination.


The software is designing to

  • Track items and ensure the smooth delivery and sorting of goods to the required destination

  • The system will also need to allow for recirculation if required when a sensor detects that a chute drop off lane is full, or if an operator is changing the sack or closed a lane for another reason such as removing items from the belt. If the conveyor cannot facilitate recirculation, then a dump lane may be required. The dump lane will also be used for any bar code misreads.

  • The system will also have functionality to facilitate the allocation of destination points in a dynamic way or changed manually by the operators being able to update a table within the controls software.

  • Integration with a light system such as below – operators can effectively close a destination point whilst changing a sack. When a chute is closed the system will either recirculate items or send them to the dump lane.

  • Recirculation, the number of times an item is recirculated (rerouted around a circular sorter system), can be managed by rules in the software, so as the system does not get blocked up with items not leaving the sorter, and subsequently restricting other items entering the sorter.


Sorter chutes – sacks – option 2 with a light system


Sorter chutes – (note the drop angle and the accumulation of cartons)


Sortation facilities are divided into five functional areas:


Each sorter system will have some or all of the following functional areas:

1. In Feed (weighing, measuring)

2. Preparation (aligning, separating, merging)

3. Identification (recognition, assigning to an order / destination point)

4. Movement around the conveyor system

5. Discharge.


see below

Circular Sorter – Continuous Loop


The sortation system can be designed to be a continuous loop - circular system, or can be a one-way system with a predetermined end point (typically a dump lane).


Other Design Considerations

1. Noise


Sorters systems can be very noisy – check the decibel levels quoted by suppliers, and even visit other sites with similar sorters to validate claims. Also, consider how over time that increased noise may result from wear on items such as bearings and motors and the other moving parts of the sorter. The noise from of one sorter type compared to another may be the deciding factor as to which option is preferred.


The Health and Safety Executive have published a guide to noise in the workplace – “Noise at work - A brief guide to controlling the risks” – see the link below:

https://www.hse.gov.uk/pubns/indg362.pdf


2. Simulation / modelling


When making an investment in sortation systems it is recommended that the sortation is simulated or modelled. Consider when and how the items to be sorted will be available, will they be cross docked, or will they be picked and packed from within the warehouse. What will the infeed rates be? Are manually loaded?


The conveyor speed and divert rates will be set within the simulation. If the outfeed locations require human intervention, then the processing rates should also form part of the simulation. The simulation should also include an allowance for dealing with misreads, and for corrective actions for items finding their way to the dump lanes. If some items are not suitable for handling through the system, e.g. oversized items then this should also be considered as part of the analysis.

3. Future Growth

As mentioned, the sorter system will require a high level of capital investment, design time and planning. At the design stage any future growth forecasts will need to be considered. If possible, the option to extend the system should be considered at the early stages. Interroll have posted the following video on YouTube, it shows have a shoe shorter being replaced with a Slide Belt Sorter. This is a good example of how one solution could be changed to another should volumes increase in the future.


https://www.youtube.com/watch?v=1JSSRwLHHg8&list=PL8Ed9xax7kIPMPnqUrolwBm9QOX9eLboR&index=1&t=218s


Alternatively, maybe space could be ringfenced in the warehouse for future expansion, or maybe the warehouse could be extended to accommodate additional sorting.

4. What different type of sorters are there?

There are many sorter types not covered in this section, only the most popular sorters have been included in no particular order:


1. Swivel (Pivot) Wheel Sorter

Swivel Wheel Sorter


Pivot wheel sorters have two sets of wheels that pivot independently and in sequence at each divert position. Adequate product spacing is required to ensure that the divert process is completed. Pivot wheel sorters can be single sided, either side, or two-sided diverts are available. Some swivel wheel sorters the wheels lift up and down when sorting, some the wheels stay level. If the wheels lift up, then this can cause stress to both the product and the equipment.


Swivel Wheel Sorter


Swivel Wheel Sorter


2. Activated Roller Belt


Intralox has developed their Activated Roller Belt (ARB) sorters. They are capable of sorting bi-directionally, at 30 degrees, and at 90 degrees and provides gentle and precise sorting of items. ARB sorters have been employed to handle cases, books, mail, totes, and polybags, and can sort virtually anything, from lightweight, letter-sized items.

Products running on ARB technology rest on free-spinning angled rollers rather than on the belt surface. These rollers extend above and below the belt surface and are positioned at an angle in relation to the direction of belt travel. Rollers are activated below the surface of the belt to move products across the belt to the left or to the right at the divert point.

Activated Roller Belt Sorter


The ARB systems can provide bi-directional sorting at rates above 100 items per minute. Right angle sorting (single-sided) at rates above 60 items per minute, this will however depend on the size and weight of the items being sorted.


3. Sliding Shoe Sorter


Shoe Sorter


Shoe sorters are suitable for sorting items such as cartons, polybags, and all other odd-sized items. Shoe sorters can sort bidirectional, at the discharge point the shoes on the belt move from either side to the other thus pushing the items from the sorter. The items can range from exceptionally light 200-gram small polybag up to 50 kg cartons. The throughput rates are a maximum of 12,000 to 18,000 items per hour (depending on the carton size).

4. Cross Belt / Slide Belt Sorter

Cross Belt / Slide Belt Sorter


The main sorter component, known as the carrier, consists of a series of carts which are actually small bi-directional conveyor belts. The configuration of the cross-belt sorter can either be in a straight line or in a loop. At the discharge point the items are conveyed at 90 degrees, either left or right to the sorter. One of the benefits of this system is that the divert locations can be close and provides a high-density space efficient sort layout.


Cross Belt / Slide Belt Sorter – Divert locations


5. Tilt Tray Sorter


Tilt Tray Sorter


A tilt-tray sorter is a high-speed, continuous-loop sortation conveyor that uses a technique of tilting a tray at a chute to slide the object into the chute. It is suitable for handling not only cartons and totes, but also soft goods that are difficult to sort with other sorter types.

6. Flatsorter / Split Tray Sorter / Bomb Bay Sorter

Flatsorter Bomb Bay


Generally speaking, a flat sorter (also known as a Bomb-bay sorter or split tray sorter) is used for the automatic sorting of relatively lightweight and flat items. These items include garments, books, pharmaceuticals, small parcels, flats, mixed mail, multi-media, jewellery, accessories and more. The machine is suitable for products that normally might not be handled on standard sorters.

Flatsorter Bomb Bay – Circular Design


Items to be sorted on a flat sorter are inducted onto a tray by a simple manual process or by an automatic induction system. When the tray is positioned above the destination the tray is opened. The content then drops flat (Bomb-bay) into the destination which can be directly into a carton/tote or into an engineered packing chute. Each of the chutes can be allocated to a specific customer order, or to a destination, or to a store.


EuroSort Push Tray System


The push tray sorter has been included for reference purposes only – the push tray sorter is another system similar in concept to a Bombay sorter, and can be used for picking operations.


7. The Tilt Sort-Bot system


A relatively new concept is the TiltSort Bot system which is similar in design to the Robots discussed in Blog “Autonomous Mobile Robots – Goods to Man”, in this application the AMR robot is equipped with a tilt tray top. Operators stand at the induction station and place an item on the top of the Robot, a camera above reads the barcode and the system directs the robot to its order chute via the shortest path. When the Robot reaches the order chute, the tray rises allowing the item to drop into the chute. Each chute represents a sortation destination. Items are collected at the bottom of the chute in bags or bulk container.

As with the Robots discussed in AMR Blogs there is no single point of failure as when a robot is unavailable the tasks are reassigned to another robot. As the system is modular it can be quickly extended, and additional robots can be added at a later date to increase the system's throughput capacities.

This system will need to be located on a mezzanine floor with operators processing the sorted loads at the lower level. These systems can also be integrated with other conveyor, other AMRs, and automated storage systems.

The TiltSort-Bot system


The TiltSort-Bot system - Induct


8. Tompkins Robotics T-Sort Sorting System

Another new concept is the T Sort system developed by Tompkins Robotics. This system requires a platform to perform the sortation however, it would be very quick to deploy and is modular so could be easily extended and additional robots added at a later stage.


Tompkins Robotics automated sorting system t-Sort



9. Mobile Belt Sortation Robots

Another new concept is mobile belt sortation system, the belts rotate at the point of load / unloading to the robot. These robots operate at ground level and apart from the fitting of QR code labels for navigation on the floor, and the creation of the infeed / outfeed locations, requires little infrastructure changes. This system is fast to implement with a quoted time of 20 days to complete the entire system, including robots and software. The system is modular so could be easily extended and additional robots added at a later stage.

Grey Orange Flexo Sortation robots



Geek Plus Robotics Sortation robots




One of the Geek Plus installations has quoted that a fleet of 200 robots, has been achieving a benchmark of 10,000 pieces per hour. 50 items / hour per robot. The maximum size of the items you can sort is approximately 50cm x 50cm up to a weight of 20kg.

5. Summary of sorters and throughput rates

This is a high-level summary of the most popular sorters used in warehouses for sortation



Note: if any of these specifications are incorrect please let me know so the data can be modified. The suppliers of each of the system has slightly different operating speeds and specifications, the items sizes and weights will also impact on the rates quoted. This is show for guidance only but demonstrates how different sorters can be applied for different product types and to achieve different throughput rates.


Note: the size of cartons can result in a variance in throughput capacities, as can the number of infeed locations.

6. Cross Dock sortation

Specialist parcel carriers have similar sortation systems as the ones described in this Blog, these operations are usually purpose designed cross dock types of warehouses designed to meet extremely high throughputs. Companies such as:

  • Royal Mail

  • DPD

  • DHL

  • Hermes

will have cross dock style parcel carrier hub designs.


Note: The Royal Mail is currently working with a supplier to design the technology for its new fully automated parcel super-hub in Warrington. Scheduled to be fully operational by early 2022, it will be the size of four-and-a-half football pitches and, once complete, handle 800,000+ parcels per day.


7. Conclusion

As with the other forms of automation discussed in my previous Blogs, the application of a sorter helps facilitate highly efficient warehouse operations. As you might have gathered from my Blogs, I am excited by all of these technologies, however, there is a right time and place for each different solution.


If you are considering using a sorter, or any other form of automation in your operations then the analysis of the current operation and assessment of alternative concepts should be assessed by impartial, independent experts. If I can help you with a sorter or any other aspect of warehouse operations design, please do not hesitate to ask for any advice. I would of course be delighted to provide a quotation to provide any assistance required.

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