robotic depalletizing unitizing unitizer

Palletizing

During the early part of the 20th century pallets were stacked by hand, but as assembly line speed increased, there became a need for faster stacking methods. Machines were developed independently by many companies, during the 50's and 60's to fulfill this need. These early machines, trying to accomplish pretty much the same task, had many commonalities. There were typically two types of machines, the first where the cases came in at an 8 to 10 foot level, were called "high level" machines. The second where the cases came in at approximately a 30" level, were called "floor level" machines. Both types typically had a pallet on the outbound side at approximately a 30" level. These early machines used Relay Logic as their means of control. As you might expect, these machines were not very flexible in the sizes and shapes of cases that they could accommodate, usually dedicated to just one case size. These early machines became known as palletizers.

In recent years, robotic palletizers have gained acceptance. Primarily due to their flexibility and size. Robotic systems provide almost instantaneous changeover from one case size to the next, with even the capability to stack differing size cases next to one another on the same pallet (mixed case palletizing). Size is also often a determining factor in picking the type of palletizer that is right for you. Robotic systems can fit into tighter areas than can a traditional palletizer. Only a few years ago, robotic systems were shied away from due to their relative slowness compared to the traditional palletizer, however in the last two to three years advances in the amount of weight that a robot can lift has dramatically changed palletizing again. Robots are now capable of lifting over 400 kg (450 kg max as of this writing), which means that they can lift entire "layers" of product in one pick/place cycle. This makes the effective time that robots can palletize in comparable to all but the highest speed palletizers.

Cases, Layers, Columns and Unitizing

Cases. The palletizers that we are considering can handle cases from only a few inches in dimension up to the size of the pallet that they get stacked onto. The product weight per case can vary from ounces up to several hundred pounds.

The ideal case for building a load is one that is rectangular rather than square. A square case can only be stacked in columnar fashion while a rectangular case can be stacked such that an "interlocking" of boxes can be achieved, providing a more stable load.

Layers (also called tiers) are what make a load stable. The ability to rotate alternate layers on the pallet help to create a very stable load. To the left you will see a few of the many possible pallet patterns available. Modern computer control systems make it possible to change layer patterns on the same pallet from one layer to the next, as the product changes. Such a pallet is termed a "mixed" pallet because it has a mixture of product types stacked upon it.

Columns. While layers make up a stable load, sometimes there are miscellaneous cases left over that simply have to be stacked. One simple method of stacking is to stack cases in columns. When stacking in columns, care should be taken to keep the height of the column small relative to the size of the cases that are being stacked. So if the cases are 20"x20"x20, stacking to a height of 40" is not a problem, however if the cases are 5"x5"x5", stacking to 40" would create an unstable load.

Unitizing. Although palletizing and unitizing are commonly substituted for one another, unitizing is the formation of a uniform load, without a pallet. Palletizing is the formation of a uniform load with a pallet.

Depalletizing

As the name implies a de-palletizer "unstacks" and separates a fully formed pallet. The purpose of a depalletizing system is usually to unstack a homogeneous pallet so the products that make it up can be reformed into a mixed pallet. As can be seen to the right the robot that is stacking the mixed pallet, is also depalletizing three other pallets. In some situations, the depalletizing robot is also the palletizing robot, but in an Order Fulfillment system, the depalletizing robot is most often a dedicated machine, handling only the unstacking of the product that goes into creating the mixed pallet.

Please follow the links below for additional information.

High Speed Palletizing

Gantry Palletizing

Robotic Palletizing