Mixed case palletizing
Mixed case palletizing builds store-ready pallets with many SKUs. How the systems work, makers and published rates, software, and pallet stability.
Mixed case palletizing builds one pallet from cases of many different products. A SKU (stock keeping unit) is one distinct product, such as one flavor in one pack size. So a mixed pallet is also called a mixed SKU pallet or a rainbow pallet. Distribution centers build them to fill store orders. Each pallet carries what one store needs.
This page explains how the systems work and who makes them. It lists the rates the makers publish. It also covers the software and the stability problems that come with mixed loads.
Why distribution centers do it
Suppliers ship full pallets of one SKU. Stores want a little of many SKUs. Dematic puts it this way: retailers receive “thousands of single SKU pallets from suppliers” and then re-assemble them “into mixed case orders for their retail stores.” Dematic says manual case picking is “labor intensive” and relies on “manual lifting of cases.”
The goal is often a store-friendly pallet. That means cases are grouped the way the store will shelve them. Symbotic says its software can sort cases “by aisle or department for easy shelf restocking or route-stop sequence for easy delivery.”
How the systems work
Most systems follow the same four steps. Dematic’s AMCAP brochure shows them clearly.
- Depalletize. Full supplier pallets come out of storage. A robot removes cases a layer at a time. Cases are then split into single cases on a conveyor. See depalletizers.
- Buffer and store. Cases wait in a high-density store. Dematic uses its Multishuttle, which stores cases “up to four deep in the rack.” Witron’s OPM system uses trays to carry cases.
- Sequence. The software releases cases in the order the pallet needs them. Dematic says cases arrive “heavy items first, fragile items last, by family group or in whatever sequence the business rules dictate.”
- Palletize. A robot cell or machine places each case. Then the pallet is wrapped. Dematic’s cell has an “integrated ring stretch wrapper.” See stretch wrappers.
Vision helps at each step. A vision system is a camera with software that finds the size and position of each case. KNAPP says on its RUNPICK system “Light curtains and camera systems check the size and the position of each item on the conveyor.” Symbotic’s FY2025 annual report lists “multiple types of vision systems” in its system.
Makers and published rates
These are the makers’ own rate claims. They use different units and different scopes. Some are per robot, some per cell, and some per whole system. Compare them with care. Real rates depend on the order mix, case sizes, and how full the buffer is.
| Maker and system | Published rate (maker’s words) | Scope |
|---|---|---|
| Symbotic | “more than 1,300 cases per hour per cell” | Per palletizing cell |
| Swisslog ACPaQ | “peak processing performance of up to 1,000 units per hour” | Peak. A 2018 Swisslog release says RowPaQ robot cells “can each” stack “up to 1,000 cases per hour.” That suggests per cell. |
| Mujin | “exceeding 1,000 cases per hour—even when handling variable SKUs and multipick operations” | Scope not stated |
| Witron OPM | “The system output amounts to more than 500 picks per hour” (2013 figure) | 2013 Witron white paper hosted by a trade magazine. We could not load a current Witron page to check it. It does not say if this is per Case Order Machine (COM) or per system. |
| Dematic AMCAP | “flexible throughput variations up to several thousand cases per hour” | Whole system, scaled |
| KNAPP RUNPICK | No hourly rate published. It “can place up to six pack units at a time per cycle.” | Per cycle |
Symbotic also says its full system output is “in excess of four million cases per week.” Witron says OPM sites range from “13,000 cases per day” to “more than 600,000 cases per day.”
Each system has limits on what it can handle. Dematic lists RapidPall case sizes from 150 × 150 × 50 mm to 650 × 650 × 450 mm. It lists case weights from 0.25 kg to 25.0 kg. Witron says OPM can stack “95% of the entire article spectrum of a typical grocery retailer.” Swisslog says ACPaQ brought automatic picking “to more than 90% of products” at one site. The rest still needs people or another process. Ask each supplier what share of your SKUs its system can handle.
Grippers
Mixed cases come in every shape, so the gripper must be flexible. Swisslog uses a “unique 4 fork gripper” on a KUKA robot. It says the robot “can grip up to four containers per movement in different formats.” Symbotic uses “pairs of robots working in tandem” with “proprietary end of arm tools.” Dematic’s RapidPall cell slides cases onto the pallet, and KNAPP’s RUNPICK rotates, tilts, and groups cases before it places them.
The software stack
Mixed case palletizing depends on software more than hardware. There are usually three layers.
WMS. The warehouse management system holds orders and inventory. It sends each store order to the palletizing system. Swisslog names its “intelligent warehouse management software SynQ” for ACPaQ.
Load building. This software decides where each case goes on the pallet. It is sometimes called a pallet build planner. Dematic says that “When orders are downloaded, the software calculates the arrangement of cases on each pallet.” KNAPP’s KiSoft Pack Master “calculates the optimal packing pattern, minimizing the number of pallets needed.” Symbotic calls its tool the Pallet Build Planner.
Machine control. This layer releases cases from the buffer in sequence and runs the robots. Dematic iQ software “directs the sequenced release of the cases from the Multishuttle buffer.”
Plans must change when things go wrong. Symbotic says that if “an expected case is missing, the software can adjust on the fly.” Mujin says its system uses “a live digital twin” to adjust “without stopping operations.” A digital twin is a live computer model of what is in the system.
Ask the supplier how the system talks to your WMS. Ask what happens when a case is damaged, missing, or the wrong size. For single-SKU loads, see pattern software.
Stability concerns
Mixed pallets are harder to keep stable than single-SKU pallets. Cases differ in size, weight, and strength. A crushed case at the bottom can lean the whole load.
The software handles most of this. Symbotic says it builds “multiple flat layers throughout the pallet as it is built.” It says “heavier, more dense cases are used to brace cases with a higher center of gravity.” Mujin says its system “evaluates case size, weight balance, and stability on the fly.”
Density is a selling point too. Symbotic says its pallets are “typically thirty to fifty percent denser than manually built pallets.” Witron claims “up to 20% more densely packed pallets or roll containers.” These are maker claims. We did not find independent tests.
Ask for sample pallets built from your real order data. Check them after a truck ride, not just at the end of the line. Set rules for crush-prone items, liquids, and chemicals.
Mixed pallets in a plant
Plants also build mixed pallets on a smaller scale. One robot cell can take cases from several packing lines and stack each on its own pallet. It can also build one pallet with several products. See multi-line robot cells and robot types and specs.
Cost
None of the makers above publish system prices. These are custom projects with storage, conveyors, robots, and software. See prices for smaller machines.
Safety
These systems mix robots, shuttles, conveyors, and lifts. Never bypass guards, interlocks, light curtains, or area scanners. Use lockout/tagout before anyone enters a cell or clears a jam, under OSHA’s 29 CFR 1910.147. Some routine jam clearing may use documented alternative measures instead, under OSHA’s narrow minor servicing exception. Robot cells follow ANSI/A3 R15.06-2025. Conveyors follow ASME B20.1. See guarding and lockout basics.
Common questions
Building one pallet from cases of many different products. Distribution centers do it to fill store orders. Each pallet holds what one store needs, often grouped by aisle. It is also called mixed SKU or rainbow palletizing.
Symbotic says its cells build mixed pallets at "more than 1,300 cases per hour per cell." Swisslog rates its ACPaQ at a peak of "up to 1,000 units per hour." Mujin says its palletizing runs at "exceeding 1,000 cases per hour." These are maker claims. Real rates depend on the order mix.
Load-building software decides where each case goes on the pallet. It gets orders from the warehouse management system (WMS). It also sets the order in which cases leave the buffer. Dematic, Swisslog, KNAPP, and Symbotic each name their own software for this.
The software places heavy cases low and fragile cases high, and builds flat layers where it can. Dematic says cases arrive "heavy items first, fragile items last." The pallet is then stretch wrapped. Dematic builds a ring stretch wrapper into its AMCAP system.
Yes, on a smaller scale. A robot cell fed by several packing lines can build pallets with more than one product. See case palletizers for multi-line robot cells.