9

482 Chapter 12: Animation
Ex a mpl e of Appl ied IK
IK structure
Animating the lamp with applied IK
The illustration demonst rates how an applied
IKanimationworks. Justasintheexamplein
Animating with Interactive IK (page 2–480),the
figure shows an IK lamp structure with its head
positioned over a spider. To m aintain the offset
distance b etween the lamp head and spider, the
actual end effector is an invisible Dummy helper
object, placed within the spider and linked to
thelampheadasachild.Thespidermovesina
straight line over 100 f rames.
To bind the end effector to the spider, click Bind,
and then drag a line between the two. Once the
end effector is bound to the spider, it will try to
match the location of its pivot point with the pivot
point of the spider.
Select the end effector and click Apply IK. The
software matches the end effector with the box
and ca lculates the IK solution for every frame.
Playback of the animation shows that the end
effector perfectly follows the box.
Note: In the above example, the end effector is
an invisible Dummy helper object, wh ich is used
to maintain the offset distance between the lamp
head and the spider.
Clearing K eys fr om Previous Animation
If you have animated any members of the IK
chain interactively, or run Apply IK previously,
the existing anim ation keys will affect the new IK
solution. Sometimes that is exactly what you want.
You can use m anual animation to subtly nudge t he
IK solution toward a particular result. However,
it is more likely that you want to remove old keys
in order to begin the IK calculations with a clean
slate.
TheClearKeysoptionintheInverseKinematics
rollout controls whether or not old move and
rotate animation keys are removed.
Constr aining the
IK Solution to Specif ic Fra mes
You use the Start and End fields in the Inverse
Kinematics rollout to set the range of fr ames used
to calculate the applied IK solution. Using these
fields, you can restrict IK solutions to specific
frames and solve for different solutions in different
time segments.
You can set the Start and End fields to include
frames outside of the act ive time segment.
YoucanalsoconstrainanIKsolutiontoframes
where a key exists for an end effector. This is
useful if you want to animate a hierarchy using end