We find that more and more companies are using industrial robots for palletising operations. Palletising robots are good at repetitive work and they are very precise.
Top 3 Advantages of Robotic Palletising System
There are a number of advantages in using an industrial robot for this work:
- Firstly as mentioned above this is a highly repetitive task which is very tiring for a human worker. The human worker building up products onto a pallet will require numerous breaks. However, the robot will be able to work 24 hours a day, 7 days a week if necessary.
- The industrial robot can lift much higher weights than a human worker. The recommended maximum weight for a human worker is 25Kg. So, this reduces when the movements require the arms to be outstretched. For example, in the case of building up large pallet formations. The industrial robot can work with payloads up to 1000Kg if necessary. Even though the most common robot types used for palletising tend to be robots with a payload capacity around 180Kg. In this case, it’s usually the required reach that dictates the robot size rather than the payload.
- The industrial robot will have a much greater palletising speed than a human can achieve. The cycle time between a product being picked up and placed and the robot returning to the pick position will be shorter than a human can achieve.
There are two different types of robot for palletising cells.
Standard six-axis robot
Dedicated four-axis palletising robot
In the case of the dedicated palletising robot, there are only four axes as opposed to six. This means that the tooling is limited in orientation to rotation solely around the vertical axis of the gripper. However, the majority of palletising operations do not require any tilting of the product. So, the advantage in using a dedicated palletising robot will be that the robot speed will be quicker and hence a reduced cycle time.
Having talked about the advantages and different robot type. Now, let’s have a look at the main elements that make up the majority of robotic palletising cells.
Main Elements of Robotic Palletising Cell
Firstly we have the robot itself. Considerations here are for payload, envelope and cycle time. In terms of the payload, this will be the maximum weight that the robot can handle. The total payload will be the weight of the product plus the weight of the gripper. The robot payload will need to be greater than the combined weight of the product and gripper. Keep in mind, if the centre of gravity is away from the centre of the mounting flange this will reduce the payload capacity of the robot.[/media]
1. Gripper for Palletising robot operations
Fitted to the robot will be some form of the gripper for picking up the product. There are different types of gripper depending on the product and the re-quired stacking pattern. In the case of a pneumatic finger type gripper, this will open around the product and have fingers that close to clamp the product. In this way, it will stop the product moving during the movement of the robot. When used this type of gripper remembers to consider the stack pattern as at the moment of placing the product the gripper will open and push any product already palletised. Usually, the gripper will release the product above its position in order that the gripper has room to open.
2. Vacuum for Palletising & Handling
An alternative solution is to use a vacuum system rather than fingers for picking up the product. In this case, the product is held in place by an array of suckers which usually grip the product from it’s upper surface. This system has the advantage that tight stacking patterns can be produced allowing the products to be placed up against product already on the pallet.
3. Cell Safety Panel
To control the complete cell a safety panel with cell control pushbuttons will be installed which is electrically connected to the robot controller. This panel will include the safety relays for the two safety circuits for the robot and any ancillary equipment. One circuit will be for the Estops, these will stop the robot in all modes, the other will be for the cell access and this will stop the robot and spindle whenever the robot is running in Auto mode.
4. Conveyor for Robotic Systems
The product will normally be delivered to one or more pickup points usually in the form of a conveyor. The management of the conveyor would normally be handled by a separate PLC to the robot as part of the machine that is manufacturing or bagging the product. The interface between the robot and the conveyor is simply the detection of the absence of the pick point being vacant with a combination of the robot clear signal and product present detection.
5. Layout Palletising Cell
The cell will also need some form of guarding which will form a room or enclosure to make sure that nobody is present whilst the robot is working in automatic. The usual layout for a palletising cell is to have two pallet locations with the robot in the middle of the two. The robot will palletise to one side and once completed will move over to palletise the second side. Then, while working on the second pallet the first pallet is removed and replaced with a new empty pallet.
Each of the pallet stations will have two sets of light curtains to protect the operator. The curtain will be active and the robot side light curtain muted whilst the robot is working on that station. If the operator were to try and enter the cell the active light curtain will stop the robot. In the case of a completed pallet, the operator will select to enter the station. Next, it will activate the light curtain on the robot side. And then, mute the light curtain at the entrance to the station. It will allow the operator to enter without interrupting the sequence. If for any reason the robot tries to enter the station during this time the active light curtain will detect the intrusion and stop the robot.