Robotic Depalletizer

Overview

A robotic depalletizer does the reverse of a palletizer: it takes loaded pallets arriving from a warehouse or a supplier and strips the cases off, layer by layer, onto a conveyor that feeds an unpacking, repacking, or production line. The job is harder than palletizing because the incoming load is not under the machine's control. Pallets arrive with cases shifted in transit, with slip sheets between layers, and sometimes mixed across SKUs, so a depalletizer leans on a 3D Vision System system to see what is actually on the pallet rather than assuming a fixed pattern.

How it works

A full pallet enters on the Pallet Infeed, a heavy roller conveyor that indexes it into the pick position and squares it with a Centering Unit unit so the robot has a known datum. The 3D 3D Vision System head looks down on the top layer, builds a depth map, and segments it into individual cases. From that map the Cell Controller decides the pick: a clean, aligned layer is lifted whole, a shifted or partial layer is taken as rows or single cases. This adaptive pick is what separates a robotic depalletizer from a fixed mechanical one, which can only handle perfectly stacked uniform loads.

The Articulated Robot is a six-axis arm on a Mounting Riser so it can reach both the top of a tall stack and the bottom of an empty pallet. Six axes rather than four are needed here because the tool must tilt and reach into a load that is not always square. Each axis is a Servo Joint of servo motor, low-backlash reducer, absolute encoder, and brake. The arm carries a large Layer-Pick Tool, a layer tool that combines a zoned Vacuum Cup Array gripping the case tops with powered Side Clamp plates that squeeze a layer for a secure lift. The vacuum is switched in zones so the tool grips only the footprint the vision system found, which lets it pick a partial layer without disturbing the rest.

The outfeed

A depalletizer creates a new problem at its output: it sets down a whole layer of cases at once, but the downstream line wants them one at a time. The Case Outfeed solves this. The robot deposits the layer on a Layer Receiver roller table, and a Singulator of diverging belts and a metering gate breaks the layer into a single-file stream on the Outfeed Belt. Getting singulation right matters as much as the pick, since a downstream filler or unpacker can only run as steady as the case stream feeding it.

Empty pallets and slip sheets

As each layer comes off, the robot also handles the slip sheets between layers, usually by switching to a separate small vacuum zone or a sheet gripper, and discards them to a chute. When the pallet is empty the Empty Pallet Stacker takes it: a lift raises each empty under a growing stack held by pawls, and a conveyor moves the finished stack out for removal. Closing this loop is what lets the cell run unattended through a shift, taking full pallets in one side and putting empties out the other.

Materials and construction

The robot links are cast aluminium on a heavy cast-iron base, and the riser is a welded steel pedestal that adds reach without adding arm mass. Joint reducers run in oil behind an Oil Seal. The layer tool frame is welded aluminium spanning a full pallet footprint, kept light because the arm pays for every kilogram of tool weight in payload. The vacuum array uses bellows foam cups that conform to slightly crushed or printed case tops, and a regenerative Vacuum Pump supplies the high flow a leaky case surface demands, unlike the low-flow Venturi a palletizer can use on clean sealed cases. Conveyors are steel roller on internal bearings, sized heavy on the infeed for loaded pallets.

Control, vision, and safety

The Cell Controller cabinet ties together a robot motion controller, one Servo Drive per axis, a cell Cell PLC, and a link to the Vision Compute. The vision computer does the heavy lifting of turning a depth map into pick coordinates, and the robot controller plans a collision-free path into the load. Safety is integral: a Light Curtain guards the pallet openings, an Area Scanner watches the floor, and interlocks on the Guard Fence gate stop the arm when opened, all through a dual-channel safety controller rated to performance level e.

Variants and use

Simple depalletizers for single-SKU uniform loads, like beverage cans, skip the 3D vision and run a taught pattern, which is faster and cheaper. Mixed-case and unstable-load depalletizing, common in distribution and grocery, needs the full vision-guided pick described here and accepts the lower rate that single-case picking sometimes forces. In service the recurring maintenance is the vacuum cups and the singulator belts, both wear items, plus periodic recalibration of the vision head to the robot frame. The robot joints are sealed and run on long oil-change intervals, so the cell's uptime is set mostly by how reliably the incoming pallets are stacked.