Manipulability Indices in Multi-wire Driven Mechanisms

Abstract

To manipulate a heavy object, one effective method is to use a multi-wire suspended system containing several cranes that can manipulate the object cooperatively. In this paper, the manipulability for multi-wire driven mechanisms is discussed. For kinematics of a multi-wire driven mechanism, we need not only the geometrical constraints of wire lengths but also the force constraints, such as the wire tension which should be always greater than or equal to zero. First, the sufficient and necessary mechanical conditions corresponding to the force constraints are shown. Under these conditions, we can obtain the “manipulability ellipsoid” of a multi-wire driven mechanism using almost the same methods as for a popular multi-link manipulator. Second, a more practical evaluation index “set of manipulating forces” is introduced and the way of calculation of this index is explained. We also derive both manipulability indices as for multi-wire suspended mechanisms in the gravity field by modeling the gravitational force as a special wire tension. Numerical examples are given to explain the proposed indices and to show their validity. The method is expected to be effective in designing and task planning of multi-wire driven systems including multi-wire suspended mechanisms.