Glossary
Inverse kinematics
Given a target pose for the end-effector, find joint angles that produce it.
Inverse kinematics (IK) is the problem of finding joint angles that put the end-effector at a desired pose in 3D space. The opposite — given joint angles, compute the end-effector pose — is forward kinematics, which is straightforward. IK is harder because solutions may not exist, may not be unique, and may not be reachable from the current configuration.
Classical solvers (KDL, ikfast, TRAC-IK, MoveIt's bio-IK) handle most cases for serial arms. For closed chains, parallel mechanisms, or whole-body humanoids, IK becomes an optimization problem solved with libraries like Pinocchio or Drake.
When a robot policy outputs end-effector deltas instead of joint deltas, an IK layer sits between the policy and the robot to translate one into the other.