1. Simulator of a SCARA Robot with LABVIEW
Ing. Luca Baglivo, Ing. Alberto Fornaser
Department of Structural Mechanical Engineering, University of Trento

2. INTRO

3. Simulink Diagram

4. Simulink Diagram

5. Jacobian evaluation
Speed of the
End Effector
Using the q it is possible to retrive the pose of the robot and the carthesian coordinate of the End Effector.
Time
Trajectory
Compensate the error of the position due to numerical integration

6. LabView Diagram

7. LabView Diagram: GUI

8. Main Logic Blocks

9. Main Logic Blocks

10. Simulator

11. Software Main Structure
The software is thought in order to pilot a robot.
It is a good approach organize the software it in the following way:
- First Task -> Move the robot to the HOME position (safe pose);
- Second Task -> Move the robot, our simulatoin;
- Third Task -> Go back to HOME.
This logic can be achieved through a Sequence structure.

12. Trajectory
Name: Trajectory.vi
-Time dependent
Input:
Center x
Center y
Radius T
Output:
x(t)
y(t)

13. Trajectory
The robot must be settled avoiding a singular initial pose.
In such way it is possible to achieve and follow a feasible path without problems A1 A2
Initial Conditions:
Q1 -> -pi/2
Q2 -> pi/2
Q3 -> 0
Geometry of the robot:
A1 -> 300mm
A2 -> 350mm
A3 -> 0mm

14. ROBOT VISUALIZATION
This Vi helps the user to understand the pose of the robot and monitor the evolution of the motion.
We need to have the full structure as output, this will simplify the programming interface a lot.
Arm_visualizer.vi

15. Jacobian and Pseudoinversion
This Vi must evaluate the Jacobian Matrix.
The input are the angles of the joints.
The output should be a matrix, and this should be inverted in a second Vi.
NB: J is related to the dimension of the joints, so it is usefull to create a Vi that output these informations.

16. Derivator
This Vi must evaluate the velocity of the End Effectot
Important: during the first loop we cannot evaluate the speed, so we need to pass directly a value.
This VI must have 2 additional imput, 2 single value ( double ).
These inputs will be used later to introduce a numeric error compensation.

17. Integrator
This VI is used after the multiplication between the presudoinverse Jacobian and the End Effector Velocity Vector. By integrating the output of that multiplication the qs (angles of the joijts) of the robot can be evaluated.
Using the Output of this Vi it is possible to connect the Robot Visualization Vi, and watch the motion of the robot directly during the processing loop.

18. Images: Some Hints
A Good methodology in LabView is to start building your Vi referring to an example, copying part of the code and then start adding your own «code».
So, how can we open an Image in Labview?
Go to:
…Program Files (x86)\National Instruments\LabVIEW 2010\examples\Vision\1. Getting Started

19. How Initialize and Load an Image
We should works with 2 images at the same time:
One is the source image
One is the destination Image
This is due to the library related to the image processing.
LabView does not allow the user to overwrite an image from the same function.

20. Camera View Simulation
Vi that simulates the camera mounted on the End Effector
Input:
- Image of the ground
- Coordinates of the End Effector
GIVEN
Vi that performs the chek of the image, the task is to identify the center of a dot seen by the camera.
Use Vision Assistant!
Vi that returns the coordiante of the identified dot in the world coordiante system

21. NB: Camera and Robot Reference Coordinate Systems are different!
Camera Simulation
The simulation is based on the identification of a region of 640x480 pixels centered and oriented according to the actual pose of the End Effector.
NB: Camera and Robot Reference Coordinate Systems are different!
Camera RCS
World RCS

22. To overcome this issue is possible to shift and rotate the image.
Camera Simulation
One of the limits of the graphic library in LabView is that you can not crop region of image using any orientation.
To overcome this issue is possible to shift and rotate the image.
ROI Centered to the origin 0,0 with dimensions 800x800 pixels
Why 800x800?
In this region i can have all the possible 640X480 sub regions with any generic orientation!
Region to Crop

23. We shift the image, not the reference system!
Camera Simulation
We shift the image, not the reference system!
Region to Crop
Region to Crop

24. Camera Simulation
Now we can apply the rotation to the image.

25. Camera Simulation
We can now Crop the image to the 640x480 region.
This is the resulting image that simulates the view of the camera!

26. Camera Simulation
NB: The rotation of the image is done around the center of the image itself.

27. Vision Assistant

28. Vision Assistant
Operation Order

29. From Camera to World RCS
Now we have the estimation of the position of the dot expressed in the camera reference coodinate system, but the robot usually works inside its own space (called also World).
We need a Vi that performs the transformation between the camera rcs and the world rcs.
Camera Reference System
Dot identified inside the image
Field of view of the camera inside the world reference system
Coordinates of the dot expressed in the world system