1 Design of a controller for sitting of infants Semester Project July 5, 2007 Supervised by: Ludovic Righetti Prof. Auke J. Ijspeert Presented by: Neha P. Garg

2 Content Introduction & Motivation Observations Hand Made trajectory Analysis of trajectory Dynamical System Further Work Conclusions Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

3 RobotCub Project Aim: study cognitive abilities of a child How: by building a 2 year old infant-like humanoid robot ICUB Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

4 Need for Locomotion Cognitive Development Explore Environment Locomotion Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

5 Real Infants Two main phases of sitting Bringing of one leg forward Movement of arm to sit on hip Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

6 Demonstration Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions Video of hand-made trajectory

7 Main Characteristics Torso Movement Leg Movement First Phase Complete Second Phase Start Arm Movement Sitting Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions Critical Phase

8 The Trajectory Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

9 Robustness Checked in only critical period Variation of the points specified for DOFs that effect critical period Trajectory is quiet robust Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

10 Robustness Right Arm Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions Point 6 Point 7

11 Robustness Torso Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions Point 6 Point 7

12 Robustness Right Leg Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions Point 3 Point 4

13 Center of Mass Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions Can information about projection of CM during sitting can be used to classify transitions as good or bad? Defining stability measure as integration of distance of center of mass from support polygon with time during sitting

14 Center of Mass Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

15 Torso Speed Can we predict sitting/falling before critical period ? Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

16 Observations from analysis Clear division of sitting in two phases Robot unstable in the second phase Robustness more important than stability Some amount of instability required for sitting Torso speed cannot be used to predict sitting/falling Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

17 Two Main Tasks Switching from crawling to sitting Designing mathematical equations for sitting trajectories Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

18 Switching from crawling to sitting When an external signal S is given, robot should switch from crawling to sitting This can be done by: Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

19 Switching from crawling to sitting This may cause abrupt shift from crawling to sitting Switching should occur only when while crawling hip and shoulder joints are moving in the same direction as they will move after shifting For this we replace S by Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

20 Switching from crawling to sitting Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

21 Dynamical System for Sitting For all of the trajectories except Left Leg (Abduc /Adduc and Rotation) the following equation can be used: Where parameter P decides when the system should start and when the system starts it goes towards can also be changed if required Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

22 Dynamical System for Sitting For example: for torso pitch P = 1 = Where S1 becomes 1 when second phase starts And is calculated as: Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

23 Dynamical System for Sitting For example: for left knee Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

24 Dynamical System for Sitting For Left Leg (Abduc/Adduc and Rotation), the movement has to be synchronized with left knee Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

25 Dynamical System for Sitting Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

26 Dynamical System for Sitting Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

27 Dynamical System for Sitting Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

28 Dynamical System for Sitting Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

29 Dynamical System for Sitting Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

30 Demonstration Crawling and Sitting using Dynamical System Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

31 Further Work Addition of sensory feedback while sitting Robot FallingRobot Falling Collection of biological data to know whether the movements while sitting are controlled by brain or spinal cord Development of controller for transition from sitting to crawling Increase in the limit up to which hip joint can be extended Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

32 Conclusions Main characteristics of sitting behavior of infants and the period of instability have been identified A controller for sitting of the robot in the same way as infants has been implemented Sensory feedback can be easily integrated by modifying values of parameter (P) according to sensory input Robot can be switched from crawling to sitting by providing an external signal Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

33 Thanks a lot! Questions? Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions

34 References [1] G. Sandini, G. Metta, and D. Vernon, “Robotcub: an open framework for research in embodied cognition,” 2004, paper presented at the IEEE RAS/RJS International Conference on Humanoid Robotics, Santa Monica, CA. [2] L. Righetti and A.J. Ijspeert. “Design methodologies for central pattern generators: an application to crawling humanoids”, Proceedings of Robotics: Science and Systems 2006, Philadelphia, USA [3] Michel, O. “Webots:Professional Mobile Robot Simulation.”Int. J. of Advances Robotic Systems, 2004, pages:39-42,vol.1 [4] G. Metta, G. Sandini, D. Vernon, D. Caldwell, N. Tsagarakis, R. Beira, J. Santos-Victor, A. Ijspeert, L. Righetti, G. Cappiello, G. Stellin, F. and Becchi. “The RobotCub project - an open framework for research in embodied cognition”, Humanoids Workshop, Proceedings of the IEEE -RAS International Conference on Humanoid Robots, December 2005 [5] MATLAB Function pchip: Fritsch, F. N. and R. E. Carlson, "Monotone Piecewise Cubic Interpolation," SIAM J. Numerical Analysis, Vol. 17, 1980, pp Introduction & Motivation Observations Hand Made Trajectory Analysis of trajectory Dynamical System Further Work Conclusions