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INTRODUCTION TO DYNAMICS ANALYSIS OF ROBOTS (Part 5)

INTRODUCTION TO DYNAMICS ANALYSIS OF ROBOTS (Part 5). Introduction to Dynamics Analysis of Robots (5).

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INTRODUCTION TO DYNAMICS ANALYSIS OF ROBOTS (Part 5)

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  1. INTRODUCTION TO DYNAMICS ANALYSIS OF ROBOTS (Part 5)

  2. Introduction to Dynamics Analysis of Robots (5) • This lecture continues the discussion on the analysis of the instantaneous motion of a rigid body, i.e. the velocities and accelerations associated with a rigid body as it moves from one configuration to another. • After this lecture, the student should be able to: • Solve problems of robot instantaneous motion using joint variable interpolation • Calculate the Jacobian of a given robot • Investigate robot singularity and its relation to Jacobian

  3. Summary of previous lecture Jacobian for translational velocities

  4. Instantaneous motion of robots • So far, we have gone through the following exercises: • Given the robot parameters, the joint angles and their rates of rotation, we can find the following: • The linear (translation) velocities w.r.t. base frame of a point located at the end of the robot arm • The angular velocities w.r.t. base frame of a point located at the end of the robot arm • The linear (translation) acceleration w.r.t. base frame of a point located at the end of the robot arm • The angular acceleration w.r.t. base frame of a point located at the end of the robot arm • We will now use another approach to solve the angular velocities problem.

  5. Jacobian for Angular Velocities In general, the position and orientation of a point at the end of the arm can be specified using

  6. Jacobian for Angular Velocities

  7. Jacobian for Angular Velocities Similarly:

  8. Jacobian for Angular Velocities Similarly: Jacobian for angular velocities

  9. Y2 Y3 X2 X3 Z0, Z1 Z2 Z3 Y0, Y1 X0, X1 Example: Jacobian for Angular Velocities A=3 B=2 C=1 What is the Jacobian for angular velocities of point “P”? P Given:

  10. Example: Jacobian for Angular Velocities

  11. Example: Jacobian for Angular Velocities

  12. Example: Jacobian for Angular Velocities

  13. Example: Jacobian for Angular Velocities

  14. Example: Jacobian for Angular Velocities

  15. Example: Jacobian for Angular Velocities What is after 1 second if all the joints are rotating at The answer is similar to that obtained previously using another approach! (refer to the example on relative angular velocity)

  16. Clarification Why r1 r2 Note: every point on the link will rotate at the same angular velocity! However, the linear velocities at different points on the link are not the same!

  17. Getting the Angular Acceleration If the joint angular acceleration for 1, 2, …, n are 0s then

  18. Y2 Y3 X2 X3 Z0, Z1 Z2 Z3 Y0, Y1 X0, X1 Example: Getting the Angular Acceleration A=3 B=2 C=1 Example: The 3 DOF RRR Robot: P What is after 1 second if all the joints are rotating at

  19. Getting the Angular Acceleration All the joints angular acceleration for 1, 2, …, n are 0s: The answer is similar to that obtained previously using another approach! (refer to the example on relative angular acceleration)

  20. Transformation between Joint variables and the general motion of the last link We can combine the Jacobians for the linear and angular velocities to get:

  21. Y2 Y3 X2 X3 Z0, Z1 Z2 Z3 Y0, Y1 X0, X1 Example: Transformation between Joint variables and the general motion of the last link A=3 B=2 C=1 Example: The 3 DOF RRR Robot: P What is the Jacobian for the 3 DOF RRR robot?

  22. Example: Transformation between Joint variables and the general motion of the last link

  23. Jacobian and Singularities We know that The above is true only if the Jacobian is invertible. From algebra, we now that a matrix cannot be inverted if its determinant is zero (i.e. the matrix is singular)

  24. Y2 Y3 X2 X3 Z0, Z1 Z2 Z3 Y0, Y1 X0, X1 Example: Jacobian and Singularities A=3 B=2 C=1 Example: The 3 DOF RRR Robot: P Investigate the singularities of the 3 DOF RRR robot

  25. Example: Jacobian and Singularities

  26. Example: Jacobian and Singularities Under these two conditions, we cannot determine the joint angular velocities using the Jacobian

  27. Summary • This lecture continues the discussion on the analysis of the instantaneous motion of a rigid body, i.e. the velocities and accelerations associated with a rigid body as it moves from one configuration to another. • The following were covered: • Robot instantaneous motion using joint variable interpolation • The Jacobian of a given robot • Robot singularity and its relation to Jacobian

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