Analyzing the physical correctness of the human motion
1. Analyzing the Physical Correctness of Interpolated Human Motion HEctor CuNat NUNez Valentijn Muijers
2. Linear interpolation of human motions Simple technique used over the past 10 years with surprisingly natural looking results… … BUT… … it has been said that the physics of the resulting motion are incorrect.
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10. 2.1. CONTACT PHASE: non-sliding foot contact Problem: Footsliding when interpolating : interpolate only the non-redundant degrees of freedom. Analysis
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12. Analysis To be physically valid ground contact should not require an unreasonably high coeffiction of friction. Coulomb friction model to analyze the ground contact. Ratio of ground reaction force and normal component should be smaller than static friction coefficient. 2.3. CONTACT PHASE: Friction cone
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14. Analysis 3. Transition between phases discontinuity in velocities not noticeable. rotation during flight phase causes problems because the orientation of the interpolated motion and original motions do not match. Solution: rotate original motions to align them with the interpolated motion a the end of the flight phase. this causes small discontinuity in velocity for CoM (see video).
Rotations are represented as Euler angles (although most of the analysis is independent of the rotation representation).
Rotations are represented as Euler angles (although most of the analysis is independent of the rotation representation).
In fact the pelvis is often chosen as the root because is generally very close to the center of mass.
(a) The ground reaction force must fall within a friction cone oriented along the contactnormal. (b) The tangential, F gr f(t) , and the normal, F gr f(n) , components of the ground reaction force. Ratio of ground reaction force and normal component of ground reaction force must be smaller than the coefficient of static friction (mu): Ft(t) / Fn(t) < mu Ground reaction force: F(t) = m * Acom(t) – m* G Where Acom is acceleration at time t of com and G is acceleration due to gravity and m is total mass
Motions with rotation during flight phase have significant discontinuities at transition between flight and stance phase because the orientation of the interpolated motion may not match that of the original motions after the flight phase. Solution: the subsequent motion of the root or center of mass in the original motions can be rotated to align them with the interpolated motion a the end of the flight phase ->this may cause a small discontinuity in velocity of com (see video)
