System description
The system includes four assemblies:
main: With an electric cabinet, 3-phase power supply, a 24V DC power supply, a PLC, a reversing motor contactor, a compressor, and a 3/2 way valve for the robot gripper.
conveyor: With a conveyor belt, a motor, and 2 sensors. There is even an empty pallet on the floor.
robot: With an ABB RobotStudio controller, an ABB IRB6620 robot, and an ideal pneumatic vacuum gripper with a sensor, the last two attached with a fixed constraint.
fence: With just some fences around the robot and the conveyor.
The system has a product entry over the conveyor which can drop boxes. The idea in this tutorial is to move the boxes to the end of the conveyor so the robot arm can pick them and finally place them on the pallet. The boxes can be palletized as you want.
Let’s download the diagrams and take a look at the configuration of the system.
As you can see the system is quite similar to the previous one. The main differences are:
The conveyor motor contactor is wired to the PLC outputs and the two sensors to the PLC inputs.
The robot controller has wired just the gripper valve and the sensor.
To allow a binary handshake between the PLC and the robot controller, the PLC output ‘out_2’ is connected to the robot controller input ‘in_1’, and the robot controller output ‘out_1’ to the PLC ‘in_2’ input.
PLC and robot handshake
If we assume that the PLC will be taking the ‘master’ role in the system, it needs to know when the robot is ready to pick a box and also needs to tell the robot when to pick. With that in mind, we can call the signals exchanged between the PLC and robot ‘Pick box’ and ‘Robot ready’. The diagram below shows this possible approach to develop a simple handshake. This could be made more advanced, but we keep it simple for the tutorial.
The diagram shows that it is possible to synchronize both controller’s programs, achieving the requested functionality, with just two signals.