8

Using IK K eyframe Parameters 759
IK Blend
The IK Blend cont rol is in t he Key Info rollout
(page 2–809)
;visiblewhenyouexpandtheIK
divider bar. You set IK Blend while in Keyframe
mode .
IK group parameters
IK Blend can be set per key for any arm or leg
track. The IK Blend setting determines whether, at
aparticularkey,anarmorlegismovingthroughit
using inverse kinematics, for ward kinematics, or a
blending of the two kinematic solutions.
An IK Blend value of 0.0 means fu ll forward
kinemat ics. The arm (or leg) is moved by
interpolating the rotations of the joints at the keys.
The hand (or foot) tends to move along sweeping
circular arcs in this case, and the motion appears
to be motivated by the apparent swinging at the
joints.
An IK Blend value of 1.0 means f u ll inverse
kinematics with the hand (or foot) being used
as an end-effector. A spline path is computed
through the keys of the hand, and the hand moves
alongthatspline.Jointanglesfortherestofthe
arm a re computed to allow t he hand to follow the
spline. The motion, in this c ase, appears to be
directed by the hand (or foot).
An IK Blend value between 0.0 and 1.0 means a
combination of inv erse and f orward kinematics;
when IK Blend is closer to 0.0, forw ard kinematics
aremoreheavilyweightedinthesolution,and
when IK Blend is closer to 1.0, inverse kinematics
are more heavily weighted.
It is best to use forward kinematics when you want
thearmstoswing,suchaswhenabipediswalking.
Inthecaseofaboxer,however,sincethehand
should f ollow a directed path when punching,
inverse kinematics should be used.
To set the IK Blend value of a key:
1.
Select a single arm or leg track by selecting one
or more parts of a biped’s ar m or leg.
The IK Blend spinner and the other controls in
the IK area are enabled only when a single a rm
or leg track is selected.
2. Set a key if one doesn’t already exist.
3. Set the desired v alue of IK Blend.
Body and Object Options
By default, Biped calculates the kinematics solution
using the coordinate system of the biped figure’s
center-of-mass, or the Body coordinate system.
This means that t he IK path of the hand (or foot)
translates and rotates with your character as it
moves. For example, the boxer’s hand trajectory
always moves relative to the weaving, bobbing,
and turning of the boxer’s body.
The Object option is used for animating dy namic
links between the limbs and other objects in the
scene.
The IK Blend control activates when a biped arm
or leg (hand and foot) key is current.
•0withBodyturnedonis
forward kinematics
(page 3–1038)
,ornormalbipedspace.