Palletizing is the process of putting items on a pallet. The process of emptying the loaded objects in the reverse pattern is known as depalletizing. A pallet is a flat, square-shaped platform used to transport and...
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A robotic palletizer is a type of palletizer that employs a robotic arm to pick, orient, and place individual products and arrange them into a single stack of load. They are the next generation of palletizers, and they will supersede conventional palletizers. Their advantages, such as lower capital cost, versatility, and multi-tasking abilities, make them the preferred choice in select applications. However, their lack of speed, product dimension tolerance, and robustness limits them from completely replacing conventional palletizers.
Like any other type of palletizers, robotic palletizers 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.
Before automatic palletizing, manual hand stacking is employed to organize products into pallet loads for storage and distribution. This method tends to be slow as 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 II. As transport of heavier loads became faster, 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 was a row-forming palletizer. In this machine, the materials are arranged on a row forming area which is then transferred to another area where layers are stacked. This is repeated until a complete stack of material is produced and ready to be placed on a pallet. This palletizing technique became the basic operation of conventional palletizers.
Robotic palletizers were introduced in the 1980s. These palletizers use a robotic arm with an end effector or product gripper that picks up the product from the conveyor or layer table then positions it on the pallet. The end-of-arm-tool can be a mechanical, suction, or magnetic gripper.
Automatic palletizers generally offer many benefits in a packaging or production line. They make manufacturing processes more efficient and eliminate the human factor that can slow down the plant‘s rate of operation. With the derived benefits, palletizers can easily surpass the required investment cost. The advantages of using palletizers include:
Palletizers eliminate manual labor for unitizing products. They are much more efficient, lift heavier loads, and perform the work faster. They also do not experience exhaustion or injury. With proper maintenance, palletizers can reliably operate 24/7. This reduces any potential bottlenecks in the packaging line.
Since palletizers are automated machines, their movements are pre-programmed and are designed to function without damaging the product. They do not need to constantly make decisions, unlike their human counterparts. This makes them less prone to errors resulting in better product handling.
When properly designed, palletizers eliminate workplace threats and hazards associated with manual labor. Manual palletizing poses falling, slipping, tripping, and crushing hazards. They also cause muscle strains due to the repetitive reaching and stacking of products. This can lead to lower back injuries and can permanently damage the health of workers.
In most applications, particularly in large packaging systems, the cost-benefit analysis of acquiring a palletizer yields positive results. Savings in operating expenses can be derived from increased throughput, low product wastage, and reduced labor costs.
If the above qualities are not enough, there are also some advantages unique to robotic palletizers. When purchasing a palletizer, the first question that comes to mind is which type of palletizer to buy. Thus, it is important to know the pros and cons of robotic and conventional palletizers. Each type has its own merits that make it suitable for a particular application. The table below compares the two pieces of equipment.
|Low investment cost for simple applications: 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 when they can cope with the required throughput.
|Better tolerance with varying packaging types: 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
|Ability to serve multiple lines: One robotic palletizer can be situated between two or more packaging lines. They can also accept multiple products with unique SKUs, each carried by individual lines. For one conventional palletizer to serve multiple lines, upstream product accumulation systems are used. Robotic palletizers eliminate this need which further cuts the investment cost.
|Higher throughput: Most conventional palletizers are used for high throughput palletizing. This is because their actuators‘ movements are much simpler than that of robotic types. Moreover, they can easily transfer and orient multiple products at once. Robotic palletizers, on the other hand, are slow if their mode of operation is individually picking and placing products. They can only increase their throughput rate by collecting multiple products at the same time.
|Versatile pattern forming: Robotic palletizers are better equipped to change pattern formation than conventional palletizers. Changing the pattern only requires reprogramming of the robotic arm‘s movement and the actuation of the end effector. There is no need to change its hardware. However, changing the palletizing pattern can cause negative effects on its throughput.
|More robust and reliable: Conventional palletizers are fit to handle heavier loads than robotic palletizers with similar capacities. In a conventional palletizer, the bulk of the load is carried by a conveyor system that easily handles weights far above the pallet load. In contrast, robotic systems have loads that are concentrated at their joints. This is especially significant for robots with articulated arms. Moreover, the joints of a robotic arm perform more movements for a given operation. Fatigue due to dynamic mechanical stresses is more evident in robotic types.
|Ability to perform secondary tasks: Robotic palletizers equipped with vacuum, magnetic, or custom end-of-arm-tools can perform additional tasks such as slip sheet dispensing, pallet placing, and wrapping. Aside from these additional functions, robotic palletizers can completely reverse their operation. This feature is seen on robotic palletizers-depalletizers.
|Easy maintenance and servicing: Conventional palletizers are easy to troubleshoot. They have several actuators that perform distinct functions. Determination of which actuator failed is accomplished by simply observing the operation of the machine. In addition, conventional types have more hardwired components than robotic types. Servicing hardwired components requires less technical specialization.
|More compact: Robotic palletizers are more compact than conventional types. They only take up the space required by the robotic arm and the staging platform for the palletized load. Conventional types have many different components such as conveyors, pushers, and ejectors; these are all required for accomplishing a single operation. This configuration takes up significant floor area and headroom. They also have multiple staging areas for layer forming.
|Easy part replacement and sparing: Most conventional palletizer actuators are on the market. These actuators are more common since their application is not limited to palletizers. Large supplies are available because of the high demand. Most manufacturers of robotic palletizers use patented parts, which usually have limited suppliers.
Robotic palletizers can be classified according to configuration and construction. Different configurations are distinguished by the palletizer‘s mode of operation. Robotic palletizers can function singly or in tandem with other units. They can also perform functions other than palletizing. Enumerated below are some robotic palletizer types divided according to configuration.
This configuration is the simplest and most common type and consists of a single robotic palletizer. This single palletizer performs a palletizing function with some designs featuring secondary capabilities such as slip sheet and pallet dispensing and stretch wrapping.
Single, In-line palletizers can service one or more palletizing lines; each line may contain the same or unique product SKUs. This depends on the design of the palletizers. Typically, they are made with articulated arms and custom-made end-of-arm-tools.
While this type of palletizing offers high versatility, its downside is its low throughput.
This palletizer type adds another layer of versatility—depalletizing. Depalletizing is the inverse process—the individual items are disassembled and separated from the unitized or palletized load. This feature is useful in applications that require the unloading of products from mixed pallets. The depalletizing robot also sorts the goods according to the product SKU.
Typically, either the palletizing or depalletizing function is done by the robotic palletizer. A single machine rarely performs both functions. Being labeled as palletizer-depalletizer usually means that the palletizer is programmable also as a depalletizer. Palletizers are used in end-of-line processes, which involve packaging and storage processes. Depalletizers, on the other hand, are used in raw material unloading and distribution. Raw materials include empty bottles, boxes, cases, and so on. The advantages offered by palletizers are also achieved when using depalletizers.
This robotic palletizer configuration involves more than one robot. Layer-forming refers to an integrated system of robots wherein each robot in the system performs a single task. A simple layer forming system is composed of two robots. One robot does the layer assembly while the other robot accomplishes the stacking. This process multiplies the throughput of the whole palletizing system.
The number and types of robots, programmed actions, and other features vary from manufacturer to manufacturer. Other designs also combine conventional and robotic palletizers. These palletizers are known as hybrid palletizers. In this configuration, layer forming is done by a conventional palletizer. Conventional palletizers are better suited for layer forming since they can easily and quickly accept incoming products from conveyor belts. After layer forming, robotic palletizers pick up the entire layer and stack them from the previous. They are much more efficient in stacking since they are designed in pick and place movements.
Mixed palletizing refers to the ability of robotic palletizers to accept different products and unitize them into a single pallet. Mixed configuration robotic palletizers are usually top-of-the-line. They usually have sophisticated programs, custom end-of-arm-tools, and sensors. They are the most versatile palletizers since they can perform minute adjustments to their arm and tooling motions without the need for reprogramming. They can adapt to the profile of the product and determine its location on the stack. Mixed configuration is useful in high SKU packaging, storage, and distribution lines.
Robotic palletizers can also be denoted according to their construction. Each type is differentiated based on its allowable movement. Thus, they have different ranges of motion. The more unrestricted their movement is, the more complex their construction becomes. Below are the four main types of robotic palletizers based on their construction.
This type of palletizer has its end-of-arm-tool that can move in three directions of space, or the Cartesian axes, hence the name. Its structure consists of beams and a telescopic mast actuated by servo motors, geared rollers, rack and pinion, chain and sprocket, or lead screw mechanisms. Cartesian palletizers are slow and limited to products with consistent weight and sizes. Their end-of-arm-tool is usually considerably basic, which is only appropriate for pick and place applications. 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-of-arm-tool or end effector assembly that is mounted on a beam that can move in one axis. The beam moves on another axis; this allows movement in the horizontal plane. To move vertically, 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 they exhibit linear movement along the three 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-type palletizer consists of an arm that is compliant or flexible in the horizontal plane but rigid in the vertical direction. This is its "Selective Compliant" characteristic. Its articulated robot arm mimics a human arm and is composed of two links attached by a joint at their ends. This joint typically has a single degree of freedom that only allows the robotic arm to extend or fold. SCARAs are generally faster than Cartesian palletizers. They can serve multiple palletizing lines at speeds of around 20 items per minute.
Articulated palletizers add two more degrees of freedom to the end effector than SCARA palletizers. They are the most sophisticated type with the closest resemblance to a human arm. Their end-of-arm-tool is mounted on a wrist that has one or two degrees of freedom. Articulated palletizers have arms that are connected by a simple joint at one end, similar to a SCARA. However, they do not have a mast. Rather, one arm is mounted onto a swivel joint with a fixed base; this allows for more flexible movement. This type is faster than the SCARA and can handle multiple production lines at about 25 items per minute.
End-of-arm-tools, columns, arms, and joints are some of the terms used in the previous chapters to describe the different types of robotic palletizers. Robotic palletizer components are more similar to robots used in automated assembly and manufacturing systems than those found in conventional palletizers. From a mechanical point of view, a robotic palletizer is an assembly of links and joints. These links and joints are specifically denoted by their role in the robotic system and their position in the assembly.
Arms are two-link mechanisms that enable the end-of-arm-tool to move along the two- or three-dimensional space by rotating, extending, or folding. The links are connected by joints that offer one or two degrees of freedom. The range of motion of the palletizer is dictated by the length of the arms and the allowed motion of the joints. Arms are exclusive to SCARA and articulated palletizer types.
Joints allow rotational or translational movement between the links of an arm. Two or more joints may be present in a palletizer system depending on the offered versatility. A robotic palletizer arm with a full, unrestricted motion typically consists of six joints. Each joint offers a single degree of freedom.
The wrist is the joint in a robotic arm that carries the end-of-arm-tool. They usually allow only rotational movement for turning the tool. Other designs can also turn the tool, granting a two-degree type of movement.
These are sometimes referred to as end effectors, which is a more general term. The EOAT is the most important part of a robotic palletizer; it is the part to which the machine‘s versatility is attributed. These devices pick up and drop the product in its appropriate location and orientation in the stack. They can be designed to handle not only finished products but also other materials such as packaging materials, wrappers, slip sheets, pallets, and so on.
The end-of-arm-tool or EOAT is the part that separates robotic palletizers from the conventional types. As mentioned in the previous chapter, this is the part to which the versatility of robotic palletizers is attributed. Below are some of the most commonly used EOATs in the palletizing industry.
These types of EOATs lift the product by clamping and gripping its sides. One part of the clamp moves while the other is stationary. Gripping action is achieved by shifting the movable part closer to the other and against the product. Clamps can collect and place multiple products with the same orientation at the same time, allowing faster throughput.
These are end effectors suitable for products that require support underneath. Because they give additional support, they can carry heavier loads without damaging the sides of the product. Their operation is similar to clamp types; they both involve using one side to push the products. As the products are pushed, they are loaded onto the fork. Like clamps, forks can collect and place multiple products at the same time.
Finger end effectors are mechanical tools that open and close in two directions. Not only do they grip the product at its sides, but they provide support underneath. This makes them more advanced than clamp and fork types. Fingers are commonly used in handling delicate products or products packed in fragile packaging materials such as paper or sheet plastic.
These end effectors use pneumatic systems that employ a venturi device to induce vacuum pressure. Vacuum types use several suction cups to hold the product on its top surface. Unlike the mechanical types, they do not cause damage to the packaging material when picking the product. They are also more reliable because of their fewer moving parts. The main disadvantage of vacuum types is their weight limitations. Also, they palletize at lower speeds since they start to lose grip when quickly accelerating the product.
This type of EOAT uses magnetic devices for lifting magnetic products or products with magnetic casing or packaging. Permanent magnets can be used since they do not continuously consume power; however, they need a mechanical device for removing the collected object. Electromagnets are preferred due to their simple operation, as the object can be lifted or dropped simply by supplying or cutting power to the electromagnet. Their suitability as a palletizer EOAT is limited since only a few products are completely magnetic. The number of applications is further reduced since magnetism can damage products or cause them to be magnetic.
Custom EOATs are uniquely fabricated tools for handling odd-shaped products. They can be equipped with a combination of mechanical, pneumatic, or magnetic actuators. This further increases the flexibility of the palletizer. Custom EOATs also allow the robotic palletizer to execute secondary tasks such as dispensing and wrapping.
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