Motion Control 1. Locomotion 1. Legged Locomotion 2. Snake Locomotion 3. Free-Floating Motion 4....
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Motion Control Locomotion Legged Locomotion Snake Locomotion Free-Floating Motion Wheeled Locomotion Mobile Robot Kinematics Models Maneuverability Motion Control
LocomotionLocomotion 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.
Locomotion - IssuesStabilityNumber of contact pointsCenter of gravityStatic versus Dynamic stabilizationInclination of terrainContactContact point or areaAngle of contactFrictionEnvironmentStructureMedium
Locomotion in Nature
Locomotion in RobotsMany locomotion concepts are inspired by natureMost natural locomotion concepts are difficult to imitate technicallyRolling, which is NOT found in nature, is most efficient
Locomotion in Robots: ExamplesLocomotion via Climbing
Locomotion in Robots: ExamplesLocomotion via Hopping
Locomotion in Robots: ExamplesLocomotion via Sliding
Locomotion in Robots: ExamplesLocomotion via Dancing
Locomotion in Robots: ExamplesOther types of motion
Locomotion ConceptsConcepts found in naturedifficult to imitate technicallyMost technical systems use wheels or caterpillarsRolling is most efficient, but not found in natureNature never invented the wheel !However, the movement of a walking biped is close to rolling
Legged LocomotionNature inspired.The movement of walking biped is close to rolling.Number of legs determines stability of locomotion
Walking of a BipedBiped walking mechanismnot 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.
Walking or rolling?structural complexitycontrol expenseenergy efficientnumber of actuatorsterrain (flat ground, soft ground, climbing..)movement of the involved masseswalking / running includes up and down movement of COGsome extra losses
Mobile Robots with legsThe fewer legs the more complicated becomes locomotionstability, at least three legs are required for static stabilityDuring walking some legs are liftedthus loosing stability?For static walking at least 6 legs are requiredbabies have to learn for quite a while until they are able to stand or even walk on there two legs.
Number of Joints of Each LegA minimum of two DOF is required to move a leg forwarda lift and a swing motion.sliding free motion in more then only one direction not possibleThree DOF for each leg in most casesFourth DOF for the ankle jointmight improve walkinghowever, additional joint (DOF) increase the complexity of the design and especially of the locomotion control.
Legged LocomotionDegrees of freedom (DOF) per legTrade-off exists between complexity and stabilityDegrees of freedom per systemToo many, needed gaited motion
Examples of Legs with 3 DOF
Legged LocomotionWalking gaitsThe gait is the repetitive sequence of leg movements to allow locomotionThe gait is characterized by the sequence of lift and release events of individual legs.
Most Obvious Gaits with 4 legs Changeover Galopping walking
Most Obvious Gait with 6 legs
The number of possible gaitsThe gait is characterized as the sequence of lift and release events of the individual legsit depends on the number of legs.the number of possible events N for a walking machine with k leg s is: N = (2k - 1)!
The number of possible gaitsFor a biped walker (k=2) the number of possible events N is: N = (2k - 1) ! = 3 ! = 3 2 1 = 6The 6 different events are: lift right leg / lift left leg / release right leg / release left leg / lift both legs together / release both legs togetherFor a robot with 6 legs (hexapod) N = 11! = 39'916'800
Walking Robots with Six LegsMost popular because static stable walking possibleThe human guided hexapod of Ohio State UniversityMaximum Speed: 2,3 m/sWeight: 3.2 tHeight: 3 mLength: 5.2 mNo. of legs: 6DOF in total: 6*3
Humanoid RobotsP2 from Honda, JapanMaximum Speed: 2 km/hAutonomy: 15 minWeight: 210 kgHeight: 1.82 mLeg DOF: 2*6Arm DOF: 2*7
Humanoid RobotsWabian build at Waseda University in JapanWeight: 107 kgHeight: 1.66 mDOF in total: 43
Walking with Three Legs
Walking Robots with Four LegsArtificial Dog Aibo from Sony, Japan
Walking Robots with Six LegsLauron II, University of KarlsruheMaximum Speed: 0.5 m/sWeight: 6 kgHeight: 0.3 mLength: 0.7 mNo. of legs: 6DOF in total: 6*3Power Consumption: 10 W
Wheeled LocomotionWheel typeStandard Wheel 2 DOFCastor Wheel3 DOFa) b)
Wheeled LocomotionWheel typesc) Swedish Wheel3 DOFd) Spherical WheelTechnically difficultc) d)
Wheeled LocomotionWheel ArrangementsThree issues: Stability, Maneuverability and ControllabilityStability is guaranteed with 3 wheels, improved with four.Tradeoff between Maneuverability and ControllabilityCombining actuation and steering on one wheel increases complexity and adds positioning errors
Wheeled Locomotion2 Wheel arrangementsa) One steering and one traction wheelb) Differential drive with COM below the axle
Wheeled Locomotion3 Wheel arrangementsc) Differential drive with third point of contactd) Two connected traction wheels plus one steerede) Two free wheels plus one steered traction wheel
Wheeled Locomotion3 Wheel arrangementsf) Three swedish or omni- d wheels: omni- directional movementg) Three synchronously driven and steered wheels: orientation not controllable
Wheeled Locomotion4 Wheel arrangements
Wheeled LocomotionUneven TerrainSuspension required to maintain contactBigger wheels can be used, but require greater torques
Adapt Optimally to Rough Terrain