When dealing with the distribution of thousands of goods per hour typically to stores or counters within stores, high-speed sorters are often used. Items such as footwear, clothing, health and beauty aids, and books, are common sorter candidates. But what happens when the cases are picked and there are pieces left over? This is called residual handling.
Sorters are fed a case of products that arrive at the induction stations where they are picked down based on that wave?s load. A wave is a selection of work to be processed within a certain time period. Waves are often successively processed to meet the whole day's requirements. When only a portion of a SKU's case is needed, the remainder returns to either a temporary residual storage buffer or is returned to its stock location. Residuals are kept in temporary storage and are reprocessed for use in later waves. The next time residuals are required for that stocking keeping unit (SKU), warehouse management software tries to take it from the buffer first.
In the past, residuals have typically been either returned to their pallet positions, or to large shelving areas where they are stored on standard static shelving units and flow racks until they are needed. Each of these methods has benefits, but they do not offer the most efficient means of processing residuals. For example, returning stock to high bay pallet positions requires the use of fork lifts in their least efficient mode--dealing with individual cases or pieces. The per-item time required in returning items to high bay storage only increases non value-added labor. Shelving is frequently used for residuals, as only one or two cases per SKU are needed. This suggests that the shallow face of shelving is appropriate for this application. However, the number of SKUs in a system often necessitates a large shelving layout. This requires large amounts of floor space, a tremendous amount of searching for items and the chance for inaccurate picking. The fact that only one or two cases per SKU is stored means that a flow rack system is not an efficient space solution either--more than half of each lane would be unoccupied. Walking time across several flow rack lanes adds to inefficiencies.
Horizontal Carousels Offer an Efficient Solution
The use of horizontal carousels is an alternative approach to the storage and retrieval of residuals. Horizontal carousels increase throughput, flexibility and product availability, while reducing labor costs and floor space.
orizontal carousels are a system of carriers that rotate on an oval track, delivering stored items to an operator on command. Integrated systems allow inventory management software to direct multiple carousels. When combined with a pick light system, which tells operators at a glance which carousel and shelf to pick from and the number of items to pick, order picking accuracy can improve to 99.99 percent.
because the carousels not being picked from are positioning themselves for the operator, throughput can increase up to 600 percent, yielding pick rates of several hundred SKU?s per hour. The high-density design of these systems reduces storage space requirements 40 to 60 percent, recovering floor space for value-added operations.
Warehouse ceiling height can be maximized by stacking of up to three horizontal carousels to take advantage of unused overhead space.
Some of the benefit is gained due to the fact of the software and controls on the carousels. Using controls and software, horizontal carousels organize pick lists automatically in order based on product location. This makes each rotation as short as possible, eliminating dwell, or waiting, time.
Why Deal with Residuals At All?
On the face of it, a least-cost approach would be placing all of the items from every partially filled case onto the sorter with the sorter driving them to one or two lanes. This residual product would be placed back onto the sorter during the next wave, and re-sorted, continuing until used. While this approach minimizes costs and requires no additional storage areas, it is not an efficient approach since every SKU is handled every wave until consumed.
Horizontal carousels allow companies to meet this challenge by bringing organization, methodology and efficiency to the residual handling portion of sorter operations, whether handled in cases or individually. Combined with low-handling-cost sorter systems, horizontal carousels provide the best handling methodology for high-speed each distribution.
In residual handling applications, horizontal carousels offer the following specific benefits:
Balanced workflow. Put-away and pick work is always available and displayed, allowing operators can switch effortlessly from picking to stocking.
Workstation flexibility. One operator can serve up to eight horizontal carousels during slow times of the day. Operators can be added as needed.
Higher productivity. Ergonomic work area minimizes operator fatigue. Safe access to tall, space-efficient carousel bins increases productivity.
No slotting maintenance required. Since this is a SKU-based system, the size of the system does not fluctuate due to fast-movers or slow-movers. Fast and slow-movers are just as likely to generate a residual case.
Better product visibility. Organizing residuals efficiently permits simple purge routines to minimize management effort and easier decision-making.
Predictable operation. The system is SKU-based. If the number of SKUs being processed each wave is roughly constant, throughput requirements are predictable. Seasonal fluctuations are confined to the number of SKUs in operation, not the quantity of what is being picked.
Stock rotation. As stock is always selected first for the next wave, it rotates efficiently.
A TYPICAL OPERATION
In a typical residual handling operation, warehouse management software sends picking demands to pallet storage for full cases, and to the horizontal carousel control system for residuals. Carousel demand is based on the number of pieces required for each SKU in that wave, less the number to be picked in full cases.
The carousel control system has knowledge of all SKUs and their locations. All carousels move to their first pick locations, and light the pick lights to indicate the shelf to pick from.
The operator picks product from the shelf, places it on the outbound conveyor and presses a task complete button. The picked-from carousel moves to the next pick, sorted by the control system to be the shortest move. The carousel may not move, as the next pick may be from the same carrier. While the first carousel moves, the operator goes to the next carousel, which displays a pick and repeats the operation. The operator continues in this way until no more picks are available for this wave.
Putting Product Into Carousels
As the wave is processed, product is transported in case quantities to induction stations at the sorter. The operator places product onto the sorter induction belt until the quantity required for that particular SKU for all orders in the wave is satisfied.
If the required quantity at the induction station is less than an exact case quantity, the operator is directed to put residual product onto a conveyor to be stored in the carousel system.
The horizontal carousel operator scans the barcode on the arriving carton. The operator is guided to an available carousel location by pick lights. The carton is placed on the carousel shelf and task completion is verified by pressing a button or scanning a label. The operator can override the guided shelf and may select an empty location manually. This process continues until all cases are put away.
Picking Methodologies
A number of flexibilities in residual handling systems residual handling applications can be completely case driven, or items can be handled individually as eaches.
Cases of product are stored and picked from carousels, regardless of the residual quantity in the case. The carousel operator always picks one case for transportation to the sorter. The required contents are removed from the case by the sorter induction operator, in the same way as whole cases from high bay storage. The case is returned to the carousel system for put away if not exhausted. The carousel system can be located remotely from the sorter, as standard inexpensive case handling conveyor is used for transportation.
In some applications, the carousel system can be located next to the sorter. The operator feeds items directly onto sorter trays, or each can be picked from carousels and conveyed the short distance to the sorter induction operator. Only the quantities required for that wave are picked from the carousel system.
The initial cases (from pallet storage) from which residuals are drawn are conveyed to the carousel system on a regular case conveyor. These cases can either be emptied into carousel locations, or the whole case can be placed onto the shelf.
The carousel residual handling system can be located away from the sorter, but still pick exact quantities of required SKUs directly into totes. The totes are sent on a standard case-handling conveyor to the sorter, where operators induct them in the normal fashion. Totes are recycled back to the carousel system for subsequent waves. This results in minimal handling for each piece, and optimizes the use of carousels where they are most proven, in each-picking applications.
Flexibility
Residual handling systems are often arranged in banks of carousels rather than in traditional pods. There can be four, six, eight, or more carousels in a bank. During slow periods of operation, one operator can handle each bank. Peak activity for a residual handling system is when product is being picked for waves while freshly created residuals arrive from the current or previous waves. Operators are presented with multiple picking choices--some or all of the carousels in a bank can offer choices at any one time. Operators can be added as necessary to meet demand, up to one operator per carousel if needed.
Residual handling applications are unique because they process the entire product for a wave at once. All picks are queued in an order that minimizes carousel rotation. There can be picks on every, or every second bin. Processing a wave means very short carousel rotation times, leading to extremely high picking efficiencies and resulting high throughput rates, in the order of several hundred picks per hour per operator. This is true even when there are only one or two carousels per operator, at peak activity periods.
System Design Considerations
When considering the installation of a horizontal carousel residual handling system, the following should be examined:
1.Number of lines and pieces processed by the sorter, per unit time (hour, wave).
2.Number of locations per SKU. A location should accommodate at least one case for a SKU, perhaps up to two cases/SKU.
3.Wave construction. Waves can be fed to the sorter singly or they may be queued (staged) due slower pallet picking needs.
4.Desired throughput requirements.
5.Space availability will influence the size and shape of the system, including individual machine specifications. As horizontal carousels can be stacked on top of each other, they can fit as necessary.
6.Where the proposed system fits. It can be located close to or remote from the sorter and can be linked by conveyor.
7.Material flow. How will product be moved into the carousel system after the residual is generated at the sorter induction station? How will selected product in the carousels get to the induction station?
8.Information flow. What kind of link will be needed to your software? Flat files, message confirmation (MQ), shared database and others are available.
9.Pick and replenish in cases, totes or singly
10.Product size and weight. Due to easy shelf adjustability, horizontal carousels can achieve greater product density across ranges of differing sizes.
11.Current operation specifications. Examine:
A.Number of pickers gathering product from shelving or high bay and delivering to conveyor.
B.Number of stockers returning product to shelving or high bay.
C.Space required and clutter generated at induction stations to stage residual cases.
In all cases, a qualified representative from a materials handling equipment manufacturer should be consulted when determining if a residual handling system is the right choice for the operation.
Horizontal carousels offer a way of taking one of the most labor and space intensive parts of a distribution operation and automating it to make it more efficient and reduce overall cost. They offer a way to reduce the overall number of people involved in handling residuals while direct, simple electronic links to the existing warehouse management packages provide seamless integration into all business activities. When this ease of integration is combined with the many advantages inherent in the equipment, the benefits are hard to ignore in the quest to improve business.