An Overview of Automated Parcel Handling System Design

With the rise of ecommerce fulfillment and direct-to-consumer marketing, there has been no other sector within the material handling industry that has experience such impact than the parcel handling segment. With existing parcel carriers increasing their business and challenged to meet rising demands, as well as new regional carriers popping up everywhere, the need to be as efficient as possible in the inbound bulk receipt process to the singulation of articles, to the manual or automated sortation and then final shipment is critical.  The key to this attaining this efficiency is automation since the sheer volume of parcels going through a parcel sort or delivery center can be way too daunting to be supported by manual operations. Automation can be applied in the inbound receipt of parcels, to the transformation from bulk flow of parcel packages into singulated flow, to sortation and then outbound shipment. Essentially transforming a manual parcel sort center into an automated cross dock that can accomplish high volume throughput.

Inbound Processing

The inbound parcel stream starts when the parcels arrive at the dock door either in the form of a full trailer load of boxed packages or large unit loads of containers or gaylords containing small packages, envelopes, polybags or other loose, small and baggy items. In order to receive into the system at a high volume and ergonomically friendly manner, telescopic extendible belts offer a wide range of benefits. For those gaylords and large containers with small items, an automated gaylord tipper is ideal for induction into the system.

Telescopic Belts

Unloading of parcels from containers in all sizes and shapes can be not only ergonomically friendly but also semi-automated with the assistance of a telescopic belt conveyor. These belted conveyors can convey packages of multiple shapes and sizes simply because it is a belt and not a roller or skatewheel conveyor. Additionally, because the units typically have multiple stages, each stage allows the belt to telescope further into the trailer or retract toward the dock doors. Therefore, when unloading a trailer full of packages, the belt is positioned in the most retracted position and associates can pull items from their location in the trailer and place onto the belt that brings them into the system. As the trailer gets emptied, the associate can extend the belt further into the trailer in order to have the infeed section close by and reduce any wasted travel. Additionally, many of these telescopic belted extendible conveyors on the inbound receiving dock have the capability of “snorkeling”. That is, the associates can also control the infeed height of the conveyor using a small control station at the infeed end. Therefore, when the associates are picking packages that are low to the trailer floor, they can adjust the infeed height to be low as well. Consequently, if the associates are concentrating on packages that are high in the trailer, they can raise the infeed elevation of the belted extendible conveyor. These features reduce many of the ergonomic challenges associated with offloading a mountain of packages in a quick and safe manner.

Gaylord Dumpers

By far, the biggest challenges in creating an automated parcel handling cross dock or sort center is due to the many small, loose items. These items, typically in the form of envelopes, polybags, jiffy bags, or other flimsy and soft small packages, are far more difficult to handle than the simple boxed package. On the front end, when receiving these items, they typically come to the sort center loaded inside large containers or gaylords. Therefore, manually pulling these items out of the containers and placing them onto a conveyor for inducting into the system would be incredibly inefficient. This is where the use of an automated tipper system coupled with a wide belted and heavy-duty parcel belt conveyor is useful. The associates forklift the containers off the trailer and place them onto the floor plate of the gaylord tipper. The gaylord tipper goes through a slow and controlled process to lift up and tilt the container so that the load of small, loose packages flow out and slide down a chute onto a conveyor belt. Although the flow of the packages is in a bulk manner, the goal of the controlled tipping process is to moderate the flow of packages down the chute and onto the conveyor belt so that it isn’t a huge wave, but instead, a gentle pour. 

Bulk Flow

Typically, the gaylord tippers induct packages at the infeed of the receiving conveyor collector belt, which eventually also collects packages from the dock door telescopic belts. Therefore, the inbound conveyor system is characterized by long, wide parcel belt conveyor running at a high speed in order to spread out the load of the bulk flow. This parcel conveyor is heavy gage steel with large drive units, high capacity drive and tail pulleys, high tensile strength belts and smooth transition points throughout. 

Singulate

After all packages of all shapes and sized are inducted into the conveyor system, the next step in the process is to arrange the packages into a back to back singulated flow for downstream sortation. This transformation of package flow is accomplished by way of an automated singulator. The use of singulators has become increasingly popular and is a vital process in high volume fulfillment and sort centers internationally and have been in use since the 1990s. However, the rise in popularity and acceptance as a viable and low risk technology has increase dramatically over the past decade. In fact, most high-speed sortation system equipment manufacturers have also developed a comparable singulation system. Therefore, there are a handful of makes and models of singulators, each with their own proprietary design that have their own features and benefits. In general, though, the singulation systems in comprised of multiple stages with each stage occupying 10’ to 50’ of space. It is common for the first stage to be some type of incline belt with a waterfall discharge belt in order to remove packages that are on top of other packages. Then a series of close-packed skewed rollers that start covering a wide width and eventually narrowing down. This causes the packages that are side by side to slide off of the side and onto a recirculation belt that is adjacent and running in the opposite direction that merges to the infeed of the first stage incline belt. Once the packages go through the skew bed and slide stages that eliminate the side by side packages, they then run through a series of gapping belts that ensure proper spacing between each package so that they are all being conveyed in a neat and orderly back to back manner that can then be processed into the sortation system. Because of all of these stages in the singulation system, when designing the sort center layout, a considerable amount of space must be dedicated to this process.  

Automated Sorting

Sorting of parcel packages of a wide range of materials, shapes and sizes in a high speed and efficient manner is constrained to only a couple types of technologies. Those being some form of unit sorters, which are arranged in a loop or in a line. The loop sorters use either a tilt tray or a cross belt in order to effectively sort the parcels whereas a line sorter uses either a sliding shoe sorter, linear crossbelt or activated roller belt technology. 

Loop Sorters

The tilt tray and the crossbelt loop sorters are very similar in use and application, with only slight differences in reasons for using one over the other. These types of unit sorters utilize a closed loop track system where carriers that have either the tilt tray or the crossbelt unit mounted on top are arranged in a back to back manner. Basically, it is a train of carriers in a continuous loop. Packages are automatically inducted onto the carrier and the control system tracks every package on each carrier. When a carrier reaches the assigned sort point for the package, it actuates and discharges the package onto the sort slide or receiving container. Because the tilt tray and crossbelt can sort to the left and right side, a large quantity of sort destinations can be accomplished. The tilt tray simply tilts left or right and allows the force of gravity to drop the package while the crossbelt actuates the motor drive to either move the belt left or right and uses this force to drive the package onto the sort destination. 

Linear Sorter

Line sorters that are found in automated parcel sort centers include the sliding shoe sorter and the activated roller belt conveyor. These types of sortation systems do not require a loop, but instead a straight line with sort points to the left or right. At the end of the line sorter, the carrying surface returns underneath and runs in the opposite direction, exactly in the same manner as a regular standard belt conveyor. Line sorters can be configured to be extremely long, spanning several hundred feet. Sliding shoe sorters use slats as the carrying surface for the packages with “shoes” placed on the left or right side of the slats. The shoes can slide in between the slats and utilize a track and guide system underneath the slats that direct the position of the shoes. When a package arrives at the sort point, a switch in the track underneath the shoes is actuated causing it to slide to the side of the divert. The shoes then come in contact with the package on the slats and pushes it off to the appropriate side. The quantity of shoes that are diverted is correlated to the length of the package being diverted. The longer the package, the more shoes are used to push the package off the sorter. 

The crossbelt line sorter behaves in the same manner as the loop sorter counterpart, however since it is a line sorter and the carriers have to return underneath, they are generally smaller carriers and do not run as fast. Otherwise, it’s use is very similar, and the application is generally when the speed requirement is not as fast or the number of sort destinations is not as high.

The activated roller belt conveyor is a technology that is based on the carrying surface containing the diverting mechanism within it. That is, the plastic belt also has small rollers or wheels that are captured withing the belt and are oriented in a different direction than the direction of flow of the conveyor. When the package arrives at the sort destination, a separate belt system underneath the plastic carrying belt is actuated which engages the rollers or wheels that are captured within the plastic belt. These wheels or roller start spinning and force the package to the appropriate side of the conveyor. This type of sortation system is very common with close sorter locations, when sorting very loose bags or if sorting a bulk flow of packages instead of singulated flow. 

Outbound

The last step in the automated parcel handling process is largely dependent on the next step in the supply chain following the parcel sort center. Understanding the next step determines the post-sort equipment selection. For example, if the next step after the sort center is a last mile delivery station, then the packages assigned for that delivery station are typically unitized in either a pallet or gaylord. However, if the sort center itself also serves as the last mile delivery station, then sorting to small containers or satchels, each of which correspond to an actual delivery route, might be more suitable. When sorting to gaylords or large containers, a sort slide that funnels packages down into the gaylord is effective. Use of gravity on a low friction slide allows the packages to transition from the sorter into the gaylord smoothly and efficiently. However, if sorting to a small container or satchel, a more positively controlled after-sort is probably most effective. This can be done with a powered strip belt divert spur or some other powered conveyance that can control the dispensing into the container or satchel. Finally, the sort spurs can further convey packages to manual pick and place stations where there might be a separate manual sorting process at the end of each of down-line. This could be where the parcels are separated from zip codes to actual delivery routes.