Control and low-level rendering issues in haptic interfaces

1. Control and low-level rendering issues in haptic interfaces University of British Columbia Department of Electrical and Computer Engineering Vancouver, Canada http://www.ece.ubc.ca/~tims IMA Workshop 9: Haptics, Virtual Reality, and Human Computer Interaction, June 14-15, 2001 REFERENCES WILL BE INSERTED LATER - PLS SEE References.pdf FOR A LIST Tim Salcudean

2. Outline • introduction and motivation • network model of haptic interaction • stability, performance specifications • controller design approaches and challenges • modelling with hybrid systems • discussion • Contributors: S.P. DiMaio, K. Hashtrudi-Zaad, M. R. Sirouspour, W.H. Zhu • List of references will be provided

3. Introduction/motivation Some haptic interfaces designed in our lab: • 3-DOF planar device • 5-DOF haptic pen • 6-DOF maglev interface

4. Introduction/motivation Haptic interface control important: • human hand characteristics difficult to match • tradeoffs? Performance optimization? • provides means for psychophysics studies • provides guidelines for design Studies of: • specific rendering problems • general methodology for coupling user to dynamic simulator

5. Network model of haptic interaction

6. Network model of haptic interaction

7. Network model of haptic interaction

8. Stability

9. Stability

10. Stability

11. Stability

12. Stability Passivity condition:

13. Stability Absolute stability conditions are satisfied.

14. Performance

15. Tradeoff example With computational of transmission delay: hybrid matrix becomes: Absolute stability condition:

16. Controller design • Two channel architectures proposed (e.g. impedance display, • admittance simulations). • Four channel architectures allow better tradeoff exploration • - Haptic interface behaves as a force or a position sensor

17. Controller design • standard linear loop shaping with nominal stability, passivity • at the environment • adaptive control • dual hybrid teleoperation • Lyapunov-based methods • kinematic scaling, impedance shaping possible • velocity control mode possible • force sensing may be replaced by observers

18. Controller design Experiments with a 3-DOF planar haptic device:

19. Controller design Impedance simulation: - slave tracks position, force returned

20. Controller design Fully transparent four-channel: - force feedforward, PD controllers for position correspondence

21. Controller design Four-channel with adaptive damping: - damping proportional to environment force amplitude

22. Controller design Absolutely stable four-channel: - reduced force channels to satisfy absolute stability criterion

23. Adaptive Teleoperation Controller • Adaptive motion/force control of master and slave robots [Zhu ‘97] h, (master) e, (slave)

24. Adaptive Teleoperation Controller where -- motion scaling parameter -- force scaling parameter -- filtered by a first-order filter [Anderson 89, Lawrence 92, Yokokohji 92, Colgate 93]

25. Adaptive Teleoperation Controller Assuming {e,h} 2nd order LTI systems + the usual on robots, we have: • stability: • transparency:

26. Adaptive Teleoperation Controller Video ...

27. Hybrid system model Consider stick-slip friction model: In practice, implemented as:

28. Hybrid system model • video...

29. Hybrid system model

30. Hybrid system model

31. Discussion / Challenges • teleoperation models and controllers applied to haptics • passivity/absolute stability allows modular software • controller analysis is now well understood for linear and some nonlinear models • controller synthesis difficult even for simple linear models • adaptive controllers complex and difficult to implement • stability/performance issues not understood for changing environments

32. Discussion / Challenges • low level programming is challenging • need model covering a wide range of behaviours in a (provably?) stable manner