User-Controlled Physics-Based Animation for Articulated Figures

1. User-Controlled Physics-Based Animation for Articulated Figures EmreAkatürk

2. Outline • Purpose of the paper • Overall System • Forward Dynamics • Collision handling • Dynamic control • Conclusion

3. Purpose of the paper • Physics based system for guided animation of articulated figures. • Why? • Physics based: Generates realistic motion but doesn’t provide control over the animation. • Kinematically controlled: User is responsible for every aspect of the motion, but may produce unrealistic results. • This work provides some of both.

4. How the system works • DOFs of a figure are classified as primary and secondary. • Primary DOFs are instrumental in achieving the goal. • Secondary DOFs move involuntary. • User defines the motion of primary DOFs kinematically.

5. How the system works

6. How the system works • User provides the system with trajectories of primary DOFs. • System computes the forces and torques that drive the primary DOFs to move along the trajectories with: MRAC(Model Reference Adaptive Control)

7. Forces • The dynamic controller generates forces and torques that move primary DOFs to produce desired motion. • There are other forces that arise due to gravity and collision.

8. Overall system

9. Forward Dynamics • With given internal and external forces, the forward dynamics simulator computes the figure motion. • The forward dynamics simulator in the system is based on Featherstone’s Articulated Body Method. • An efficient recursive algorithm, no preprocessing.

10. Collision Handling - Detection • Collisions between segments are detected by examining segment geometry, orientation and position. • A bounding box check algorithm is used.

11. Collision Handling - Response • Divided into two stages: impact and contact • Impact: • Velocity of the involved objects change instantly but do not move. • Simulator is restarted if objects are not seperated, then contact stage starts. • Contact: • A spring-damper is used for every contact point.

12. Dynamic Control • MRAC(Model Reference Adaptive Control) • Easy to implement • One basic controller can be used to control a variety of dynamic systems. • User doesn’t need to set non-intuitive parameters. • User has direct control over the ideal behaviour of the system.

13. MRAC

14. Conclusion • Work provides: • A physically correct, user controlled animation system. • A fast collision algorithm. • An efficient forward dynamics simulator.