1. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose Using Wave Variables for System Analysis and Robot Control MSc. Lei Ma 27 May, 2004

2. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Contents Introduction to teleoperation Concept of passivity Wave variable: idea, definition, characteristics conclusion

3. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Telerobotics: System construction A master (local) device, A slave (remote) device, A communication channel. Communication channel

4. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik General description Human operator as present of high-level control of activities; Both master and salve have own control systems; Human operator requires information: Proper user interface; Data feedback from the slave site: forces applied to the environment, relevant positions of the slave, graphical video data, tactile or acoustic information.

5. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik The master Typical features of the master are: Capability of assigning tasks to the slave and providing the operator with relevant information about the task development TELEPRESENCE: Implementative solutions: joysticks and/or consoles; Different types of signals may be reflected by these devices to the operator. Capability of acquiring and processing data from both the operator and the slave.

6. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik The slave directly interacts with environment for task execution. A robotic system for the interaction with the environment and the execution of the task planned by the operator; Signal acquisition and processing; Capability data processing.

7. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik The communication channel represents the link between the master and slave sites. Main drawback. Time delay in the transmission of signals: physical delay in the transmission line (e.g. in a long satellite communication), limited bandwidth of the hardware. The time delay, in some case not constant, can originate noticeable instability problems. A very common choice in practical applications is to transmit velocity to the slave and force to the master.

8. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Application space underwater hazardous environments production security simulators …

9. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Rotex: ROboter Technology EXperiment Robotic arm for intra-vehicular activities developed by DLR, Germany. Successfully used in the mission of the space-shuttle COLUMBIA in 1993. Variety of operational modes: teleoperation on board,teleoperation from ground using predictive graphics, sensor-based off-line programming. Performing three significant tasks: assembly of a grid, connection/disconnection of an electrical plug, grasp of a flying object.

10. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Transmission delay over Internet Discussion of time delay of 0.1~several seconds because: Human operator as slowest element has reaction time of ~0.1 sec; Teleoperation not possible with delay more than 10 sec

11. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Problem statment Slave manipulator follows motion of the master properly. Force applied to the environment fedback to mater properly.

12. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Problem statement: stability A control system is in equilibrium if, in the absence of any disturbance or input, the output stays in the same state. A control system is stable if the output eventually comes back to its equilibrium state when the system is subject to an initial condition. Example: inverted pendulum.

13. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Problem statement: passivity Loosely said, a system is passive if it absorbs more energy than it produces. Power entering the system: P = x T y A system is said to be Passive if : P = x T y = dE store /dt+P diss The power is either stored or dissipated. Or: the system cannot generate energy and provide only as much as stored initially. E store : energy storage

14. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Passivity A system is passive if energy supplied by it is limited to the initial stored : Say if a system absorbs energy then P is positive, otherwise P is negative. Or: the system itself can not produce any energy.

15. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Properties of passive systems A passive system is stable; Connection of passive elements remains passive; A passive system is said to be lossless if P diss =0; It is dissipative if P diss >0.

16. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Passivity of communication channel in teleoperation Assume no initial energy stored in the communication channel, the channel is passive if P not lower than zero.

17. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Time delay causes instability P is no longer guaranteed to be semi-negative, thus passivity Is also not guaranteed.

18. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Wave variable: idea Virtual tool for modifying the entire dynamics of the teleoperator system into a simple and well know form; Shows both basic physical characteristics like inertia and stiffness ; Delay presents as a passive element in the system; As the delay increases the tool becomes softer and / or heavier; A large delay can thus be tuned into either a heavy drill or a soft sponge. Both provide a heavy versus soft tradeoff appears naturally as a tuning parameter; In real time, if no contact is made, for example during a virtual inspection, the virtual tool should be tuned to a soft sponge making quick motions easy; In close proximity to a desired contact location, the tool should be adjusted to a heavy and stiff appearance, allowing good force clarity under slow speed.

19. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Wave variable: definition U denote the forward (right moving) wave; V denote the backward (left moving) wave.

20. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Passivity of wave systems Assume u provides input and v contains output, and there is no energy stored initially, the system is passive if If v=u(t-T) True if v is limited to bound of u Energy due to delay T is stored, time delay is a passive element

21. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Wave variables in teleoperation

22. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Passivity in telemanipulation Energy stored, communication channel is passive and lossless.

23. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Remarks Wave variables themselves have no physical meaning. Symmetry – u and v are distinguished due to sign of F. Hybrid encoding: When in contact, wave command produces force, When in free space, causes motion. Move or push commands – energy may be converted to either potential or kinetic energy as needed. Wave impedance e.g. given u, lager b leads to higher weight for velocity dx/dt, so that more force and lower velocity reconstructed, system appears more damped.

24. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Comparison of power and wave variables

25. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Wave response: Extreme example of a string v = -u v=u

26. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik More wave responses

27. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Conclusion Wave variable method Applies well to inherently passive system – robots; Shows power gain with non-passive systems, there for possible to design power reduction element to counteract energy production and force global passivity; A delay is passive when it occurs in wave variables while not passive when it effects power variables; In case of teleoperation delay effectively occurs in software level, wrap delay with proper encoding to achieve passivity; Provides new perspective on system and makes further methods possible (filtering, prediction,…).

28. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik References and links: A detailed and intuitive introduction to passivity, wave method and teleoperation: http://telerobotics.stanford.edu/publications/Niemeyer_PhD_Thesis.pdf http://telerobotics.stanford.edu/publications/Niemeyer_PhD_Thesis.pdf Univ. Bologna: http://www-lar.deis.unibo.it The Haptics Community Web Site: http://haptic.mech.northwestern.edu/http://haptic.mech.northwestern.edu/ Rotex: http://www.robotic.dlr.de/telerobotics/rotex.htmlhttp://www.robotic.dlr.de/telerobotics/rotex.html

29. Seminar Telematiksysteme zur Fernwartung und Ferndiagnose MSc Lei Ma Informatik VII: Robotik und Telematik Thank You ! Question ?