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This article provides comprehensive knowledge about palletizers. Read further and learn about:
A palletizer is an automated material handling machine used to stack and orient several individual products into a single load for a more convenient and economical method of handling, storage, and shipment. Palletizers are usually part of a bigger packaging process where functions such as weighing, counting, sorting, labeling, metal detection, and wrapping are integrated. Some of these functions may be integrated into the palletizing machine itself or done by separate equipment.
Palletized products take advantage of the concept of unit load. Unit load refers to the assembly of materials combined for efficient handling. It is faster and more economical to move a large, single unit instead of several small individual items. Finished goods are not designed and built to be handled and shipped separately. These are usually placed in boxes, cases, trays, and crates that are then combined into a single unit supported by pallets or roll cages. The former ones are referred to as secondary unit loads, while the latter ones are tertiary unit loads.
Products are stacked by the palletizer into a pallet, hence the name. Pallets are flat, stable structures made of wood, plastic, paper, or steel. They have notches or openings which forklifts and hand pallet trucks use for lifting and moving the load. These openings make a pallet either a two-way or a four-way describing forklift entry. Most pallets can handle loads of up to one ton with an area of about a square meter. Below are the standard measurements of pallets.
DimensionsOther palletizers can also stack items on a slip sheet or conveying surface. These are known as unitizers. Unitized loads do not require a pallet. In other references, palletizers and unitizers are used interchangeably.
There are three main types of wood or plastic pallets and one for cardboard.
GMA is the most common pallet. Typically 40x48 with notches in the side so they can be picked up from the side.
CHEP is the second most common pallet. Typically 40x48 with blocks on all sides so it can easily be picked in either direction. These reliable pallets can be easily identified by the blue paint on the pallet‘s sides.
PECO is a newer company in the pallet world with a very similar service as CHEP. The pallet can be identified by the red paint on the pallet‘s sides.
Pull Board is a corrugated sheet with two 3" tabs typically on the adjacent side. Fork trucks with a special attachment clamp the tab or pushe the load on or off the forks. Used for hygiene and/or space savings in transportation. Removing a pallet saves 5" of space per load. This can add an extra layer or two in a truck resulting in substantial savings.
Other palletizers can also stack items on a slip sheet or conveying surface. These are known as unitizers. Unitized loads do not require a pallet. In other references, palletizers and unitizers are used interchangeably.
There are different pallet patterns that companies may require.
The benefit of this pattern is that the column stacked on the bottom provides a significant amount of stacking strength needed in the warehouse. Pallets may be stacked up to four loads high in a warehouse. Load strength comes from the corners of the boxes that line up vertically. The interlocked portion at the top provides stability for the unwrapped load to be transported with a fork truck to a wrapper.
Before automatic palletizing, manual hand stacking is employed to organize products into pallet loads for storage and distribution. This method tends to be slow where a lot of work is needed relative to the output. Pallets and pallet handling became one of the most important logistics tools in the early 20th century, particularly during World War 2. As the transport of heavier loads at a faster pace became progressive, a need for new material handling and storage capabilities followed.
The first mechanical palletizer was designed and built by Lamson Corp. in 1948. The palletizer built was a row-forming palletizer. In this machine, the materials are arranged in a row forming area. The arranged materials are then transferred to another area where layers are stacked. This is repeated until a complete stack of material is produced ready to be placed on a pallet.
In 1970, as the need for faster logistics grew, so as the need for faster palletizing. This brought the launch of an in-line palletizer. Instead of the intermittent motion of the row-forming, the in-line palletizer uses a continuous motion to guide and orient the product into its position on the layer forming platform. This is done until the layer is complete which is then placed onto a pallet.
Robotic palletizers were then introduced in the 1980s. These palletizers use a robotic arm with an end effector or product gripper which picks up the product from the conveyor or layer table and then positions it onto the pallet. The end-of-arm tool can be mechanical, suction, or magnetic grippers.
Palletizers are mainly divided into two categories: conventional and robotic palletizers. Both can receive products at high and low elevations. High elevations typically range between 84" to 124", while low elevations are 30" to 36". Conventional palletizers are then divided into floor- (low-) level and high-level palletizers.
As mentioned earlier, these palletizers have an infeed level of 30" to 36". As the product flows through the infeed conveyor, a turning device or conveyor orients the product before moving it onto the row forming area. Products are arranged on the row forming area until a row is completed. The row is then pushed onto the layer forming area. Once a complete layer is formed, it is again pushed forward to the stripper plate. The products are raised or lowered and then pushed onto the pallet or previous layer. The stack remains static during the load building process. This process is done until a pallet load is complete. The completed pallet is moved onto the pallet discharge conveyor. The discharge level is typically at 18".
Floor-level palletizers are less expensive and simpler in construction which takes less floor space than high-level palletizers. Since most parts are at floor level, maintenance of the machine is faster and straightforward because of the easy access to its parts. Also, the machine‘s operation can be monitored easily by an operator since most moving parts are at eye-level. Regarding its integration to the rest of the packaging line, since there is no change in elevation of the infeed conveyor, floor-level palletizers are ideal for coupling packers and sealers.
These palletizers have an infeed level of 84" to 124" or higher. Similar to floor level palletizers, the product goes in as transported by the infeed conveyor to a turning device or conveyor that rotates the product into the appropriate orientation before it is pushed to the row forming area. Again, products are arranged until a row is completed. The row is then moved to the layer forming area. Once the layer is formed, it is ready to be pushed into the pallet or stack. The palletizer raises or lowers the stack for each layer that is placed on the pallet. Its capability to raise and lower the stack is its main difference with low-level palletizers. The completed stack is then lowered to the discharge conveyor. The discharge elevation of high-level palletizers is typically between 18" to 30". In most installations, an elevated operators‘ platform is constructed together with the machine.
High-level palletizers are used when there is enough space for an inclined conveyor where the packer and sealer are located at some distance. In contrast with floor-level palletizers, high-level machines have a higher throughput relative to the size of the machine making the utilization of floor space more efficient. High-level palletizers are used for throughputs of around 40 to 50 items per minute, regardless of the packer or sealer discharge elevation.
A conventional palletizer is composed of many parts; some are static, while others are moving. Some parts can be integrated with the palletizer itself or installed as separate equipment.
Bags coming from the packaging units and sewing machines are usually in a standing position. These bags are then set or knocked down by the knockdown conveyor to prepare it for palletizing.
This may be an integrated or separate machine used as an assuring measure to check the weights of bagged products before storage and distribution.
Like the checkweigher, this device can be an integrated or separate machine from the palletizer. The metal detector detects any ferrous, non-ferrous, or stainless-steel contaminant in the product.
Detected products that are either off-weight or contain metal contaminants are then moved by the reject conveyor onto a staging area or platform.
Products may enter at different sides of the palletizer. These palletizer infeed types are side, rear, and front infeed. This applies to both floor-level and high-level palletizers.
To form the pattern properly, the bag flattener flattens and shapes the bags to their proper height.
As the product is fed by the conveyor into the palletizing machine, the product is oriented into its appropriate orientation before proceeding into the row forming area. Turning devices can be a turn shoe, cushioned turn, turntable, or soft turn. The turn shoe and cushioned turn gently bump the product to change its orientation by 90°. The turntable raises the products and rotates at +90°, -90°, or 180°. Soft turn devices use two sets of rollers using variable frequency drives (VFD). Different speeds of the rollers allow the product to rotate +90°, -90°, or 180°.
These are mechanical devices used to form the appropriate pattern in the row forming area by creating side-to-side gaps. Stops are actuated by pneumatic valves and cylinders which are controlled by programmable logic circuits (PLC). Changing forming patterns only requires modification of the software controls with no hardware changes.
Similar to stops, these mechanical devices are used in pattern forming by creating a front and back gap in the pattern. When a layer is completed, it is pushed onto a stripper plate or apron. This is then moved onto the pallet. When the stripper plate is in position on top of the pallet or stack, a gate comes down blocking the movement of the layer. The stripper plate is then pulled back leaving behind the layer on top of the stack. The pusher gate holds a layer in position before release.
This part allows front and back gaps to be created without the use of a pusher gate. As the stripper apron opens in the middle, gaps are created while the layer is being placed to the stack below.
From the name itself, this part dispenses and conveys pallets for continuous operation of the palletizer. When one unit load is completed, a new pallet is fed by the pallet dispenser. A pallet dispenser usually has 10 – 20 pallets stored in a pallet magazine.
Some materials, especially bagged products, require slip sheets in between layers. A slip sheet dispenser efficiently places a slip sheet using a venturi vacuum system.
This part is used to transfer finished unit loads into a platform where the goods are picked up by forklifts or hand pallet trucks for storage.
This is where operators troubleshoot, fine-tune, or reprogram the palletizer machine and its automatic accessory components. The main part of the control panel is the PLC which opens and closes circuits as directed by the machine‘s programming.
These types of palletizers use robotic arms to move the end effector and perform pattern forming. Robotic palletizers were further divided into cartesian, gantry, SCARA, and articulated. Flexibility and range of movement differ from each type.
This type of palletizer has an end of arm tool that can move in three directions of space, or the Cartesian axes X, Y, and Z, hence the name Cartesian. Its mechanical structure consists of beams and a telescopic mast usually actuated by servo motors. This type of robotic palletizer is slow and is used for products with consistent weight and sizes. This is generally the cheapest type of robotic palletizer suiting single line speeds of up to 10 items per minute.
A gantry palletizer consists of an end effector assembly that is mounted on a beam that can move along one axis. The beam moves on another axis allowing movement in the X-Y plane. To move along the Z-axis or up and down, the end effector assembly can be a telescopic or articulated arm that can fold or extend vertically. Gantry palletizers are also considered Cartesian palletizers since movement is linear along the Cartesian axes. They perform pick and place operations but are generally slower than Cartesian robots. Moreover, these machines tend to be larger, thus more expensive. The upside in using these types is its capability to lift heavier loads.
A SCARA is a robot that consists of an arm that is compliant or flexible in the X-Y plane (left, right, forward, and back direction) but rigid in the Z-axis (top and down direction). This describes its "Selective Compliant" characteristic. Its "Articulated Robot Arm" is similar to a human arm composed of two links attached by a joint at their ends. This allows the robotic arm to extend or fold. SCARAs are faster than Cartesian palletizers. SCARAs can serve multiple palletizing lines at speeds of about 20 items per minute.
This palletizer type adds two more degrees of freedom to the end effector, in contrast with SCARA palletizers. Articulated palletizers have arms that are connected by a simple joint at one end, similar to SCARA. However, they do not have a mast. Rather, one arm is mounted into a swivel joint with a fixed base which allows more flexible movement. This type is faster than the SCARA that can handle multiple production lines at about 25 items per minute.
Robotic palletizers differ in the manner in which they perform pattern forming. Looking at their construction, it is obvious that robotic palletizers use completely different parts. Parts like the check weigher and metal detector are applied but installed as separate equipment. Below are the common parts of a robotic palletizer.
This part carries the end effector, enabling it to move in a linear direction at only one axis. Motion is provided by servo motors through rollers and rail, rack and pinion gearing systems, or chain and sprocket drives. This part is seen on Cartesian and gantry palletizers.
This part is mounted on a fixed base and carries the beam or arm and end effector assembly. Hydraulics, servo motors, or chain drives raise or lower the connected parts, enabling them to move up and down.
These are usually two-link mechanisms which enable the end effector to move on the horizontal plane by rotating, extending, or folding.
These parts allow rotational movement between other parts. Two or more joints may be present in a palletizer system depending on the offered versatility.
These are sometimes referred to as end-of-arm tools. The end effector is the most important part of a robotic palletizer assembly due to its versatility, in contrast with conventional palletizers. These devices pick up and drop the product in its appropriate location and orientation on the stack. They can be designed to handle different products with a common tool. Moreover, they can be fitted with the option to pick pallets out of a pallet rack in lieu of a separate pallet dispenser. It can also pick slip sheets, tier sheets or top caps out of a dispensing rack. Both of these rate-dependent options are a great way to better utilize a robot.
Below are the most common types of end effectors.
These types lift the product by clamping and gripping the sides. Clamps can collect and place multiple products with the same orientation at the same time, allowing for faster throughput. They are most suitable in picking stable products with attributes not conducive for vacuum. These are typically used with HSC (case with no top) or display cases.
Fork tools are commonly used to pick products that are delicate, unstable, HSC (case with no top), display case, warm/hot shrink wrapped product, or other products where gentle handling is required. The location where the product is picked typically has special cut outs that allow the tool to go underneath the product, then lift and cradle it for gentle handling. A clamp tool can be added to the fork tool for stability when the robot moves.
Finger end effectors are mechanical tools that open and close in two directions. They also provide support underneath the product. These are commonly used in handling bags.
Vacuum end effectors are the most common end-of-arm-tools for picking up RSC cases. These tools can be zoned to pick multiple cases at one time. A blower can be used to generate a high volume of vacuum that is necessary to lift boxes that are made of very thin porous corrugated from recycled material. This option can be used rather than using a venturi system that is dependent on plant air (not always reliable) and can‘t always produce the volume of air needed.
Bag end-of-arm-tool is used to pick up large bags of product one at a time. Able to add a slip and/or tier sheet between layers, depending on speed requirements.
This type of end effector uses electromagnets to gather products. Magnetic end effectors are used in stacking and palletizing canned goods.
Though conventional palletizers are the earlier form of palletizing technology, the newer robotic palletizers are not a complete replacement. Each type of machine has its own merits which suit a specific application. Moreover, because of the vast array of industries that require palletizers, there is no specific design that can suit all. Below are the advantages of using either conventional or robotic palletizers.
Advantages of Using Conventional Palletizers:
Conventional palletizers form the unit load by turning and pushing the product to its desired location and orientation without the need to pick up and place the product. Thus, varying the packaging dimensions or packaging types will not affect the handling of the palletizer. If modification is needed, this can be done by adjusting the controls through its program. No hardware modification is needed.
Robotic palletizers are slow if their mode of operation is by individually picking and placing products. They increase their throughput rate by collecting multiple products at the same time. However, this offers less flexibility than conventional palletizers which can be modified to change pattern forming configurations without sacrificing throughput.
Advantages of Using Robotic Palletizers:
For simple palletizing solutions, a robotic arm can be employed where speed is not a critical factor. Using a robotic arm eliminates the need for multiple conveying systems, turning mechanisms, stoppers, gates, and so forth. Thus, robotic arms are a cheaper option provided that it can cope with the required throughput.
One robotic palletizer can be situated between packaging lines and can handle more than one type of product. For one conventional palletizer to serve multiple lines, upstream product accumulation systems are used. Robotic palletizers eliminate this need which cuts investment costs.
Robotic palletizers are better equipped to change pattern formation as compared to conventional palletizers. However, changing the formation can affect its throughput.
This type of palletizer brings the best of both worlds: the speed and reliability of conventional palletizers, and the flexibility of robotic palletizers. Hybrid palletizers use conventional methods of row forming by using turning devices and stoppers, while a robotic arm picks up the whole layer and places it on the pallet or stack. This eliminates the disadvantage of high-level palletizers which need products to be moved up by a conveyor while maintaining its advantage of higher throughput.
Another variation of a hybrid palletizer is robotic pattern forming. While a robotic arm can do layer handling, it can also be used to orient and position the products to the layer forming area. Once the layer is complete, the conventional palletizer places it on the stack while performing other functions such as pallet and slip sheet feeding.
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