Presentation on theme: "Capture Point: A Step toward Humanoid Push Recovery"— Presentation transcript:
1Capture Point: A Step toward Humanoid Push Recovery Jerry Pratt1, John Carff1, Sergey Drakunov1, Ambarish Goswami21Florida Institute for Human and Machine Cognition2 Honda Research InstituteHumanoids 2006December 6, 2006
2Capture Point: A Step toward Humanoid Push Recovery
3Some Push Recovery Approaches Replan trajectories.Solve Constrained Optimization Problem.Machine Learning.Heuristics based on intuition and simple models.
4Outline Push Recovery Overview Our Approach to Push Recovery. Simulation Examples.Ongoing and Future Work.
5Importance of Push Recovery Bipedal robots in human environments:Bumping into objects.Incidental contact when walking down a sidewalk.Tripping over cluttered floors.Contact during sports.Intentional pushes.Method of human input interface.Understanding and Assisting HumansFalls are a major cause of injury.
6Theoretical and Practical Difficulties of Push Recovery Non-linear dynamicsMulti-variable dynamicsLimited foot-ground interactionHybrid dynamics (dynamics are both continuous and change discretely during steps)Quick detection of push required.Fast reaction speed required.Relatively large actuator power required.
7Human Push Recovery Strategies Move the Center of Pressure, predominately through ankle torques.Accelerate Angular momentum by “lunging” and “windmilling”. [Video]Take a step. [Video]Combinations. [Video1, Video2]
8Why these Strategies Work Broomstick (Inverted Pendulum) AnalogyTightrope Walker Analogy
9Using Angular Momentum effectively increases the size of your footprint [Popovic, Goswami, Herr IJRR2005]
10Outline Push Recovery Overview Our Approach to Push Recovery. Simulation Examples.Ongoing and Future Work.
11Capture Points and Capture Regions (Quick Definition) Capture Point: Point that the biped can step to and stop in one step without falling down.Capture Region: Set of all Capture Points.F
12Balance Strategy 1: Center of Pressure Kinematic WorkspaceOf Swing LegSupportFootCapture Region
13Balance Strategy 2: Accelerate Angular Inertia (“Windmill” or “Lunge”) Kinematic WorkspaceOf Swing LegSupportFootCapture Region
14Balance Strategy 3: Take a Step Kinematic WorkspaceOf Swing LegSupportFootCapture Region
15Balance Strategies 4,5,6: Multiple Steps, Run, or Fall Kinematic WorkspaceOf Swing LegSupportFootCapture Region
16How to Compute Capture Points? Simple Models with Closed-Form Solutions.Numerical SearchLearning
17Computing the Capture Point for the Linear Inverted Pendulum (Kajita and Tani 1991) Model
18Computing Capture Points for the Linear Inverted Pendulum plus Flywheel Model
19Deriving Linear Inverted Pendulum Plus Flywheel Dynamics using Similar Triangles MgFxz0X- /Mg
20Flywheel is torque-limited due to motors. Computing Capture Points for the Linear Inverted Pendulum plus Flywheel ModelFlywheel is torque-limited due to motors.Flywheel is position limited to model humanoid upper body.Greatest effect the flywheel can have is through a bang-bang torque profile so that the flywheel accelerates and decelerates as quickly as possible, stopping at its maximum or minimum angle limit.
21Computing Capture Points for the Linear Inverted Pendulum plus Flywheel Model Bang-bang torque profileSolve for TR1 and TR2 given initial and final states of the flywheel.Since dynamics are linear and torque profile has Laplace Transform, everything can be computed in closed form.
28Applying Linear Inverted Pendulum based Capture Point to 12 dof 3D model
29Stepping Stones by “guiding” the Capture Point to the Desired Stepping Point
30Take Home Message 1Precise foot placement is not necessary for push recovery, but good foot placement is.If any point of the foot is placed inside the Capture Region, the humanoid can stop.Larger feet and/or more angular momentum increase robustness to poor foot placement.
31Take Home Message 2 Simple Models can be Useful! Understanding of the fundamental principles.Control Algorithm Development.
32Future Work Apply to a real humanoid. Derive closed form calculations of Capture Points for arbitrary CoM height trajectory.Numerically compute Capture Regions for complex models and compare to simple models.Extend to persistent pushes.Expand techniques to other aspects of walking:Dynamic Turning.Rough Terrain.
33Capture Point: A Step toward Humanoid Push Recovery Jerry Pratt1, John Carff1, Sergey Drakunov1, Ambarish Goswami21Florida Institute for Human and Machine Cognition2 Honda Research InstituteHumanoids 2006December 6, 2006