Manikin Time; Development of the Virtual Manikin with External Root and Improved Inverse Kinematics

摘要

Simulating manual assembly operations considering ergonomic load and clearancedemands requires detailed modeling of human body kinematics and motions, aswell as a tight coupling to powerful algorithms for collision-free path planning.The focus in this thesis is kinematics including balance and contact forces, andergonomically preferable motions in free space. A typical manikin has more than100 degrees of freedom. To describe operations and facilitate motion generation,the manikin is equipped with coordinate frames attached to end-effectorslike hands and feet. The inverse kinematic problem is to find joint values suchthat the position and orientation of hands and feet matches certain target framesduring an assembly motion. This inverse problem leads to an underdeterminedsystem of equations since the number of joints exceeds the end-effectors’ constraints.Due to this redundancy there exist a set of solutions, allowing us toconsider ergonomics aspects and maximizing comfort when choosing one solution.The most common approach to handle both forward and inverse kinematics isbuilding a hierarchy of joints and links where one root must be defined. A popularplace to define the root is in a body part, e.g. in a foot. This leads toa two-step procedure; (i) determining if re-rooting is necessary, (ii) solving theinverse kinematic problem using the Penrose pseudoinverse.In this thesis we propose using a fixed exterior root by introducing six additionalparameters positioning the lower lumbar - three rotations and three translations.This makes it possible to reposition the manikin without a series of re-rootingoperations. Another important aspect is to keep the manikin, affected by internaland external forces and moments, in balance. However, by utilizing the exteriorroot and its added degrees of freedom it is possible to solve the balance, positioning,contact force and comfort problems simultaneously in a unified way.A manikin was implemented, and some specific test cases demonstrate the applicabilityof the presented method and also use randomized goals to show thegenerality of the solver.