How Do You Stack Up? A Look Into Robotic Palletizing

Once a manufactured product is complete and ready for shipment, it often needs to be stacked onto pallets for convenient distribution. Without automation, workers have to physically handle and stack the product before shipment, requiring a large amount of labor that often leads to injury and discomfort.

Automated palletizing offers significant savings in labor on an assembly line, by stacking the product without the use of human labor.

 

First, Are Robots Necessary for Palletizing?

Some palletizing processes can be done with hard automation and don’t require a robot. Heavy, large bags, such as cement or grain, can be palletized with a series of sliding horizontal doors and a mobile conveyor chute.

For such simple systems, a PLC or relay control system can be enough to run the machinery. These simple palletizers only work if there is a consistent product that does not change size or stack patterns, such as boxes that are always the same size.

There is a big step in difficulty when moving to more complicated stack patterns or varying products, a robot is often necessary to handle these changes. A robot has the ability to change product placement based on information programmed or sent into the system via external sensors. They can also be used to stack different types of products if they are equipped with a gripper that can handle more than one configuration of a product.

 

The Importance of Efficient Movements

The programming that controls the palletizing process can make or break a system when it comes to efficiency. A system that optimizes movements between jobs can significantly improve the amount of time it takes to create a full pallet of product.

 

Figure 1. A mobile robotic palletizing solution, designed for quick changes in production. Image used courtesy of Control.com - Robotiq at a trade show

 

When programming the system, it is important to consider intervals in which the system will experience downtime in productivity and use that time for other tasks. For example, if the robot has placed all the products from the feed system, it can use that downtime to place a slip sheet on a pallet that needs one.

The most efficient way to do this would be to wait until there is a lag in the product before placing the slip sheet, to keep the system from backing up on the other lanes.

T-cart systems allow for the robot to stack multiple lanes of product simultaneously. When dealing with a system with a T-cart, programming should keep downtime to a minimum and stage pallets in order to avoid delays.

 

System Reset and Placement Count Override

A major improvement in any palletizing system is to include a placement count override, which allows a way to reset the counts on each lane, or for any part of the system.

For instance, if a box falls out of the EoAT (end of arm tool), the operator should have the ability to adjust the placement count on the pallet so that boxes do not have to be stacked physically in the empty slot.

An effective tool that makes the reset process user-friendly is an HMI touch screen. HMIs can be programmed with buttons to reset each lane to zero, or to add/subtract layers in the stack on the pallet.

This makes an operator's task much easier and safer than if they had to manually adjust the count. Otherwise, the operator would have to create a short stack and finish the stack by hand or go inside the cell to make the configuration of the pallet the same as the current count in the robot after an error in stacking.

 

Figure 2. Robotic palletizing involves customized grippers for individual boxes and packages. Image used courtesy of Control.com - Columbia/Okura at a trade show

 

With an HMI, the system offers more flexibility in the way it can stack products. It allows for versatility in the types of products moved simultaneously through one lane. The operator can simply type in updated product dimensions, the number of layers, and slip sheet placements, as needed.

The robot can then offset its pick and place positions to match the box changes, allowing for a much more versatile system. With this arrangement, future products can easily run through the system with little interference.

 

PLC Controlled vs. Robot Controlled Palletizing

PLCs run ladder logic to perform tasks in an automated system. Essentially, a PLC runs a sequential code that executes line by line down the “ladder” of the program structure.

 

PLC Control

This makes them very efficient in the logical processing of sequential tasks. For example, after the robot grabs boxes to palletize them, the PLC can be programmed to begin the next task in the operation, such as signaling for more product to be pushed down the line for staging.

 

Robot Computing

Robots generally use some form of structured text code as their processing language. The use of these languages allows the robots to process information faster than a PLC when computing different processes during production.

The robot has an edge over the PLC during the stacking portion of the palletizing process. It is easier for the robot to compute where the stack layer is, where the next place position will be, and keep track of slip sheet layers all at the same time. Since it can record positions and computations in the background, there is no need for a sequential process, allowing for a more efficient system.

 

Figure 3. Partnerships between robot and software companies can help optimize motion paths and decrease cycle time. Image used courtesy of Control.com - Yaskawa at a trade show

 

AI Computing System

Some palletizing operations do not rely on the robot or an external PLC controller. Instead, all the data acquisition from cameras and scanners is collected in a central computer, and through the help of efficient algorithms (usually AI), motion paths and destination points can be computed in real-time.

The major advantage of this system is that for different products, a different motion path may be more efficient. If the computer can continually compute the quickest path, the cycle time is always kept to a minimum, even with mixed SKU payloads.

 

Palletizing with Speed and Safety

The best systems are not always the fastest ones. Instead, they are the ones that can complete the main task, plus all peripheral tasks, with a minimum amount of downtime that affects the processes up and downstream. Most often, a combination of control systems are leveraged to provide the best palletizing workflow for each kind of product.

 

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What’s the most surprising fact you’ve learned about automated palletizing?

 

Original article published April, 2020