Inverse Kinematics of Discretely Actuated Ball-Joint Manipulators Using Workspace Density
We present a workspace-density-based (WSDB) method to solve the inverse kinematics of discretely actuated ball-joint manipulators. Intuitively speaking, workspace density measures the flexibility of a robotic manipulator when the end-effector is fixed at a certain pose or position. We use the SE(3) Fourier transform to derive the workspace density for ball-joint manipulators and show that the workspace density has a concise and elegant form. Then we show that the state for each joint is determined by maximizing the workspace density of subsequent sub-manipulators. We demonstrate our method with several numerical examples. In particular, we show that our method can provide a solution that approximately minimizes the deviation of the end-effector and its computational complexity is linear with respect to the number of joints. Hence our method is very efficient in solving the inverse kinematics of redundant discretely actuated ball-joint manipulators. In addition, we prove that the solution space of our method is reduced from the rotation group SO(3) to a one-dimensional interval.