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Motion Control

Motion Control. Locomotion Legged Locomotion Snake Locomotion Free-Floating Motion Wheeled Locomotion Mobile Robot Kinematics Models Maneuverability Motion Control. Locomotion. Locomotion is the act of moving from place to place.

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Motion Control

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  1. Motion Control • Locomotion • Legged Locomotion • Snake Locomotion • Free-Floating Motion • Wheeled Locomotion • Mobile Robot Kinematics • Models • Maneuverability • Motion Control

  2. Locomotion • Locomotion is the act of moving from place to place. • Locomotion relies on the physical interaction between the vehicle and its environment. • Locomotion is concerned with the interaction forces, along with the mechanisms and actuators that generate them.

  3. Contact Contact point or area Angle of contact Friction Environment Structure Medium Locomotion - Issues • Stability • Number of contact points • Center of gravity • Static versus Dynamic stabilization • Inclination of terrain

  4. Locomotion in Nature

  5. Locomotion in Robots • Many locomotion concepts are inspired by nature • Most natural locomotion concepts are difficult to imitate technically • Rolling, which is NOT found in nature, is most efficient

  6. Locomotion in Robots: Examples • Locomotion via Climbing

  7. Locomotion in Robots: Examples • Locomotion via Hopping

  8. Locomotion in Robots: Examples • Locomotion via Sliding

  9. Locomotion in Robots: Examples • Locomotion via Dancing

  10. Locomotion in Robots: Examples • Other types of motion

  11. Locomotion Concepts • Concepts found in nature • difficult to imitate technically • Most technical systems use wheels or caterpillars • Rolling is most efficient, but not found in nature • Nature never invented the wheel ! • However, the movement of a walking biped is close to rolling

  12. Legged Locomotion • Nature inspired. • The movement of walking biped is close to rolling. • Number of legs determines stability of locomotion

  13. Walking of a Biped • Biped walking mechanism • not too far from real rolling. • rolling of a polygon with side length equal to the length of the step. • the smaller the step gets, the more the polygon tends to a circle (wheel). • However, fully rotating joint was not developed in nature.

  14. Walking or rolling? • structural complexity • control expense • energy efficient • number of actuators • terrain (flat ground, soft ground, climbing..) • movement of the involved masses • walking / running includes up and down movement of COG • some extra losses

  15. Mobile Robots with legs • The fewer legs the more complicated becomes locomotion • stability, at least three legs are required for static stability • During walking some legs are lifted • thus loosing stability? • For static walking at least 6 legs are required • babies have to learn for quite a while until they are able to stand or even walk on there two legs.

  16. Number of Joints of Each Leg • A minimum of two DOF is required to move a leg forward • a lift and a swing motion. • sliding free motion in more then only one direction not possible • Three DOF for each leg in most cases • Fourth DOF for the ankle joint • might improve walking • however, additional joint (DOF) increase the complexity of the design and especially of the locomotion control.

  17. Legged Locomotion • Degrees of freedom (DOF) per leg • Trade-off exists between complexity and stability • Degrees of freedom per system • Too many, needed gaited motion

  18. Examples of Legs with 3 DOF

  19. Legged Locomotion • Walking gaits • The gait is the repetitive sequence of leg movements to allow locomotion • The gait is characterized by the sequence of lift and release events of individual legs.

  20. Most Obvious Gaits with 4 legs Changeover Galopping walking

  21. Most Obvious Gait with 6 legs

  22. The number of possible gaits • The gait is characterized as the sequence of lift and release events of the individual legs • it depends on the number of legs. • the number of possible events N for a walking machine with k leg s is: N = (2k - 1)!

  23. The number of possible gaits • For a biped walker (k=2) the number of possible events N is: N = (2k - 1) ! = 3 ! = 3 2 1 = 6 • The 6 different events are: lift right leg / lift left leg / release right leg / release left leg / lift both legs together / release both legs together • For a robot with 6 legs (hexapod) N = 11! = 39'916'800

  24. Walking Robots with Six Legs • Most popular because static stable walking possible • The human guided hexapod of Ohio State University • Maximum Speed: 2,3 m/s • Weight: 3.2 t • Height: 3 m • Length: 5.2 m • No. of legs: 6 • DOF in total: 6*3

  25. Humanoid Robots • P2 from Honda, Japan • Maximum Speed: 2 km/h • Autonomy: 15 min • Weight: 210 kg • Height: 1.82 m • Leg DOF: 2*6 • Arm DOF: 2*7

  26. Humanoid Robots • Wabian build at Waseda University in Japan • Weight: 107 kg • Height: 1.66 m • DOF in total: 43

  27. Walking with Three Legs

  28. Walking Robots with Four Legs • Artificial Dog Aibo from Sony, Japan

  29. Walking Robots with Six Legs • Lauron II, University of Karlsruhe • Maximum Speed: 0.5 m/s • Weight: 6 kg • Height: 0.3 m • Length: 0.7 m • No. of legs: 6 • DOF in total: 6*3 • Power Consumption: 10 W

  30. Wheeled Locomotion • Wheel type • Standard Wheel • 2 DOF • Castor Wheel • 3 DOF a) b)

  31. Wheeled Locomotion • Wheel types • c) Swedish Wheel • 3 DOF • d) Spherical Wheel • Technically difficult c) d)

  32. Wheeled Locomotion • Wheel Arrangements • Three issues: Stability, Maneuverability and Controllability • Stability is guaranteed with 3 wheels, improved with four. • Tradeoff between Maneuverability and Controllability • Combining actuation and steering on one wheel increases complexity and adds positioning errors

  33. Wheeled Locomotion • 2 Wheel arrangements • a) One steering and one traction wheel • b) Differential drive with COM below the axle

  34. Wheeled Locomotion • 3 Wheel arrangements • c) Differential drive with third point of contact • d) Two connected traction wheels plus one steered • e) Two free wheels plus one steered traction wheel

  35. Wheeled Locomotion • 3 Wheel arrangements • f) Three swedish or omni- d wheels: omni- directional movement • g) Three synchronously driven and steered wheels: orientation not controllable

  36. Wheeled Locomotion • 4 Wheel arrangements

  37. Wheeled Locomotion • Uneven Terrain • Suspension required to maintain contact • Bigger wheels can be used, but require greater torques

  38. Adapt Optimally to Rough Terrain

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