Palletizing machines overview

This section of the website includes three broad categories of packaging machine.

Palletizers

Depalletizers

Pallet wrapping machines

Palletizers

Palletizers are machines that load packages or products on to a pallet for transport and storage. Products handled range from boxes, bags and shrink-wrapped trays to bricks, empty bottles and cans. Palletizers come in a wide variety of configurations but can be placed in two broad categories.

Layer palletizers form and transfer complete layers of product to the pallet in succession. There are two broad configurations. (a) Low level palletizers where individual layers are raised or lowered on a flat plate (often called a stripper plate) for transfer to a stationary pallet. (b) High level palletizers where individual layers are formed and transferred to the pallet at an elevated level with the empty pallet raised and then lowered progressively as the pallet build proceeds.

Robot palletizers apply robotic technology in machines to lift and place single or multiple items on to a pallet. Two specific types of robot are typically used. (a) Articulated robots (for example six axis industrial robots) programed and equipped with tooling for lifting products. The robot can also lift and place empty pallets and insert separating sheets between layers. (b) Cartesian (orthogonal axis) robots custom built, programed and equipped with tooling similar to an industrial robot. Two common types of construction are gantry robots and single column robots.

This classification is not rigid. For example a robot might form each layer as a component of a layer palletiser or a lift and place cartesian type palletizer might not necessarily use robotic control methods.

In recent years robot palletizers have taken a very large share of the market for palletizers because of their flexibility of operation, relative ease of installation and adaptability to new products. However, for high volume applications a layer palletizer is generally capable of production rates higher than a single robot.

Below are illustrations and animated diagrams with descriptions of typical of layer and robot palletizers.

Low level layer palletizer

This diagram shows a typical low level type layer palletizer with infeed and discharge conveyors for pallets. Product is conveyed to the row forming area which can be at any height within the limits of the hoist. Before each row is formed boxes can be turned if required by the layer pattern for stacking on the pallet. Successive rows are pushed on to the stripper plate to form a complete layer or, as an intermediate stage, on to a separate forming bed which allows the palletizer to operate at a higher cycle rate. The stripper plate carrying the complete layer moves vertically up or down and laterally to a position directly above the empty pallet or previous layer where it retracts and deposits the layer. Side compactors and a backstop steady and support the layer during transfer. The stripper plate then moves up or down to receive the next layer. A device to lift and place separating sheets between layers is often installed.

view an animated diagram of a low level layer palletizer

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High level layer palletizer

This diagram shows a typical high level type layer palletizer with infeed and discharge conveyors for pallets. The empty pallet is raised to the level where the first layer of product will be transferred. Product is conveyed at high level to the row forming area. Before each row is formed boxes can be turned if required by the layer pattern on the stacked pallet. Successive rows of product are pushed on to a layer forming bed to form a complete layer. The complete layer is then pushed on to closed shutter plates which open laterally to deposit the layer on the empty pallet or previous layer. Twin separating roller shutter curtains are also commonly used for this operation. Side compactors steady and support the layer during transfer. The pallet load then lowers by one layer height to receive the next layer and the cycle repeated until the pallet load is complete and discharged.

view an animated diagram of a high level layer palletizer

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Articulated robot palletizer

This diagram shows a typical articulated robot having four degrees of freedom in a palletizing cell building two separate pallet loads of boxes supplied on a common conveyor. The robot also places separating sheets between each layer. The gripper head is a suction lifting device suitable for light loads. Side clamps or hooks are used for lifting heavier loads. The gripper head can also rotate the box to provide an interlocked stacking arrangement. Layout of palletizing cells using articulated robots requires careful consideration of safety in terms of the operating envelope of the robots. Application of collaborative robots is increasing where operators can safely intervene manually during normal operation of the robot.

view an animated diagram of an articulated robot palletizer

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Gantry (Cartesian) robot palletizer

This diagram shows a three axis Cartesian type robot with a gantry structure in a palletizing cell forming two pallet loads from separate product conveyors. The robot also transfers empty pallets from a free-standing pallet stack to the pallet loading positions. Pallet loads and empty pallet stacks are transported to and from the cell by lift trucks. The gripper head uses suction to lift boxes and hooks to lift pallets. Side clamps could be used to lift heavier boxes. The gripper head can also rotate a box to provide an interlocked stacking arrangement. Gantries can extend across many product lines with individual robot units dedicated to specific zones.

view an animated diagram of a gantry robot palletizer

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Depalletizers

Depalletizers are machines that unload multiple items stacked in layers on a pallet, typically empty containers, for example supplying bottles, jars and cans for filling on a packaging line. Depalletizers can be placed in two broad categories.

Sweep-off depalletizers push containers horizontally off the pallet load. In a low-level type machine the layers transfer from a stationary pallet to the discharge conveyor via an intermediate transfer plate that moves between levels. In a high-level type machine the pallet load rises progressively and the layers sweep directly on to the discharge conveyor.

Lift-off depalletizers lift containers with a gripper head and place them on a discharge conveyor. The pallet load can be stationary or progressively raised. Nowadays the basis of most lift-off type depalletizers is either a Cartesian (two or three axis) robot or an articulated industrial robot. Lift-off depalletizers are able to lift complete layers or individual rows of containers and are particularly suitable for lighter weight containers which can be supported by vacuum. Other gripping methods can be used depending on the material and form of the containers.

Sweep-off depalletizer

This diagram shows a typical low level sweep-off depalletizer unloading a bulk pallet of empty bottles with the pallet load conveyed to the unloading position. Bulk loads are normally protected for transit and storage by plastic film which is removed manually or by automation. Sheets or trays that separate layers are also removed manually or by automation as each layer is unloaded.

The depalletizer hoist lifts the sweep frame and the transfer plate which rises and falls sequentially between unloading and discharge levels. To unload a layer of bottles the sweep frame lowers to surround the layer on the pallet. Steady bars mounted on the frame move inwards to stabilise the containers. The frame then sweeps the containers on to the transfer plate. The hoist moves to the level of the discharge conveyor where the frame sweeps the containers off the transfer plate on to the conveyor. When all layers are transferred the empty pallet is discharged by conveyor, typically to a pallet stacking unit.

A high level sweep-off depalletizer sweeps layers of containers directly on to a discharge conveyor from a pallet load raised sequentially by a hoist. Cycle times are faster than a low level sweep-off depalletizer but because containers are discharged at a much higher level than the pallet infeed conveyor this configuration is not always compatible with the layout of the downstream packaging line.

view an animated diagram of a low level sweep-off depalletizer

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Lift-off depalletizer

This diagram shows a typical lift-off type depalletizer unloading a bulk pallet of empty cans. This example is a Cartesian (two axis) robot, single column type machine. The pallet load is conveyed to the unloading position. Bulk loads are normally protected for transit and storage by plastic film which is removed manually or by automation. Sheets or trays that separate layers are also removed manually or by automation as each layer is unloaded.

Layers are lifted sequentially from the pallet by the gripper head and transferred to the discharge conveyor. The empty pallet is discharged on a conveyor, typically to a pallet stacking unit. A lift-off depalletizer can also lift and place individual rows of containers on to a single line conveyor. Various methods are used to grip containers in the lifting head. For example, vacuum grippers are suitable for lightweight containers, magnetic grippers for cans with ferrous content and bars for gripping rows of bottles by the neck.

Articulated robots are also widely used for lift-off depalletizing and offer advantages of greater flexibility in their application.

view an animated diagram of a lift-off depalletizer

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Pallet wrapping machines

Pallet wrapping machines wrap a pallet load with flexible film for protection and stability during transport and storage. There are two broad categories of machine based on the method used to apply the film:

Stretch wrapping machines apply film stretched by tension during application, most commonly in a spiral wrap around the sides of the load. Application is often supplemented by a top sheet of film applied and secured during wrapping. Common types are: rotating table, rotating arm, and rotating ring machines. Stretch hood machines pull a stretched hood of film over the pallet load. As it descends, the hood grips tightly on the load.

Shrink wrapping machines place film loosely over the load and then shrink the film around the load by applying heat. Placement and shrinkage of film can be carried out in a single machine or in separate units. Heat can be applied from a horizontal frame surrounding the load, from vertical columns adjacent to the load or in a chamber or tunnel oven. The shrink hood machine which places a pre-formed hood over the load combined with an integral or downstream shrink frame is the most common type. The curtain wrapping method is also used for applying shrink wrapping film to pallet loads. This method is more widely used for shrink wrapping of bulk products.

Wrapping a strap around each layer of product in a pallet strapping machine is also a method of stabilising some pallet loads but provides no external protection.

Rotating table pallet stretch wrapper

This diagram shows a typical semi-automatic, free-standing rotating table type of pallet stretch wrapper, where the pallet load is placed on the turntable by truck. An operator attaches the film from the film reel mounted on the carriage to the base of the stationary load or around a peg on the turntable. The start control initiates rotation of the turntable and upward movement of the film carriage with film pulled from the reel to provide spiral wrapping of the load. Powered rollers on the carriage can pre-stretch the film for economy and a tighter wrap. Wrapping progresses automatically to the set top limit and then descends and stops at the base. The operator cuts and tucks the film tail into the load or pallet. Pressure from a suspended, freely rotating plate on the top of the load (not shown) can stabilise lightweight loads during operation.

This type of semi-automatic machine is very widely used for low to moderate throughputs and is extremely flexible in terms of application and location. Fully automatic versions have conveyors for infeed and discharge of pallet loads and automated attachment, cutting and sealing of film.

view an animated diagram of a rotating table pallet stretch wrapper

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Rotating arm pallet stretch wrapper

This diagram shows a typical fully automatic rotating arm type pallet stretch wrapper. The pallet load is conveyed to the wrapping position and the vertical arm carrying the the film carriage starts rotating. The film tail held in the adjacent gripper bar is cut after the first rotation and wound into the wrap. Wrapping in a spiral pattern progresses with film pulled from the reel as the arm rotates. The film carriage rises to a set point and then descends to the base.

Powered rollers on the carriage can pre-stretch the film for economy and a tighter wrap. Pressure from a pad lowered on to the top of the load (not shown) can stabilise lightweight loads during operation. A dispenser for a top sheet of film can also be fitted with the sheet secured by the side wrap at the top. When rotation stops at the base the adjacent heat sealing unit swings inward and welds the film web to the wrap. A bar swings up to cut the web and grips the film tail from the reel ready for the next cycle.

This type of wrapping machine is capable of high rates of production, typically for loads conveyed directly from a group of palletizing machines. A configuration offering a higher cycle rate comprises two opposed vertical arms with a film carriage mounted on each arm.