PRACTICAL P1: A robotic manufacturing cell - Qualitative analysis and programming

The problem

Consider a robotic cell composed of:

  • a UR3 robot,
  • a conveyor that moves the parts from location B to location A, and that must be stopped when a part reaches A,
  • a presence detector that senses if a part is at location A.
../../_images/ur3_cinta.jpg

Task 1

Consider first the task where:

  • The system is initialized with a part at B, and the conveyor is moving.
  • There is only one part in the system.
  • When the part is at A, the robot picks it and places it at B.
  • The conveyor only needs to start moving when the part is at location B, in order to move it towards A.

Task 2

Consider now the task where:

  • The system is initialized with at least one part at B, and the conveyor is moving.
  • There can be more than one part in the system (a human operator may put or remove parts on the conveyor as desired).
  • When a part is at A, the robot picks it and places it at B.
  • The conveyor must be moving all the time except when there is a part located at A or during the place operation.
  • It is assumed that there is always room to place the part at B.

PN modelling

Exercise 1

Model task 1 using Petri Nets.

Exercise 2 (optional)

Model task 2 using Petri Nets.

Programming the robot

Exercise 3

Program the UR3 robot to execute task 1.

To start with, do the following steps:

  1. Test the robot motions:
    • Move manually the arm in freedrive mode to a home configuration
    • Move with the arrows the arm in Cartesian coordinates of the Base and of the Tool
    • Write a program to move the robot from the home configuration to another configuration, and execute it only once (set the continuous execution to off).
  2. Test the I/O:
    • Move the conveyor by setting the digital output 0 (or the analog outputs 1 and 2, depending on the belt used).
    • Put an object in front of the sensor to verify it has been detected by the sensor (digital input 1).
    • Write a program to start the conveyor and stop it when the object has reached the sensor (execute it only once)
  3. Test the opening and closing of the gripper with the UR cap.

Now, program task 1 and enjoy!

Exercise 4 (optional)

Program the UR3 robot to execute task 2.

Use a thread to command the conveyor.