Constrained motion models for insertion/extraction operations applied to the Hermes robot arm: a feasibility study

Abstract

During operations with a manipulator arm situations will occur where the manipulator end-effector is, or comes, in contact with its environment. In case of the HErmes Robot Arm HERA, contact with the environment may well be planned. For instance, operations like insertion and extraction of a tool from a tool rack, grappling of an Orbital Replaceable Unit (ORU), or insertion/extraction of an ORU from the payload rack will lead to planned contact. Another operation where planned contact is made is force exertion at a surface. Simulation of mechanical systems that are in contact with their environment is demanding, and is well known to be liable to numerical instabilities. A method recently developed at NLR allows for stable numerical integration of dynamical systems subject to constraints. The models (of the constraints) capture restrictions on, for instance, the position and orientation of the end-effector of the manipulator. Previous studies with (simple) mechanical systems as well as with the complicated dynamics model of the HErmes Robot Arm showed good results. A logical follow up of these studies is the simulation of insertion/extraction operations. This is the main objective of the present study: show the feasibility of modelling insertion and extraction operations using constrained motion models.