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Joints An IK joint controls how an object transforms with respect to its parent.
You specify joint behavior with settings in three categories:
■ Object Pivot Point The location of an object’s pivot point defines where
joint motion is applied.
■ Joint Parameters Changing the IK settings in the Hierarchy command
panel determines the direction, constraints, and order of how the joint
operates.
■ Parent Pivot Point The location of an object’s parent pivot point defines
the origin from which the joint constraints are measured.
The commands you use to place the pivot points for both the object and its
parent are described in
Adjusting Pivots on page 3345.
Start and End Joints The start and end joints define the beginning and end
of an IK chain managed by the IK solver. The hierarchy of the chain determines
the direction of the chain. The pivot point of the end joint is displayed as the
end effector, when end effector display is enabled.
Kinematic Chain Inverse kinematics calculates the position and orientation
of objects in a kinematic chain. The kinematic chain is defined as any part of
a hierarchy under IK control. The IK chain starts with a selected node and
consists of a start joint and an end joint. The base of the chain is either the
root of the entire hierarchy, or an object that you specify as a terminator for
the chain. The kinematic chain is defined when you apply an IK solver to a
chain, or when you create a bone chain with an IK solver automatically applied.
Goal The goal is used by the HI Solver to manipulate the end of the chain.
When the goal is animated, the IK solution attempts to match the end effector
(pivot point of the last child in the chain) to the goal position. When using
an HD Solver, the end effector fulfills the same function as the goal.
End Effector For any IK solution, you explicitly move a control object. IK
calculations then move and rotate all other objects in the kinematic chain to
react to the object you move. The object that you move is the goal, in an HI
Solver or IK Limb Solver, or in the case of an HD Solver, an
end effector on
page 7963.
Preferred Angle Determines which direction a joint will bend. The preferred
angle establishes a base angle between chain elements when an HI Solver is
applied. The IK Solution seeks this angle in calculations.
Solver Plane and Swivel Angle Manipulator A plane can be defined between
the start and end joints, which aids in controlling the IK solution. Adjust or
animate the solver plane by changing the swivel angle manipulator when in
3378 | Chapter 15 Animation