Cable-based Robot Manipulators with Translational Degrees of Freedom

Abstract

Cable-based robots build upon mechanisms that not only use rigid links in their structures but also utilize unilateral force elements such as cables to deliver the desired motion. Cables may be either connected to active winches to provide a variable length and hence to actuate the mechanism or may be only to provide a kinematic constraint to eliminate an undesired motion of the endeffector. Manipulators in which the cables have variable lengths are usually called cable-driven or wire-driven manipulators. Cable-based manipulators posses several advantages over conventional serial/parallel link manipulators including: 1. Large workspace: An active winch can provide a large range of length change on the cables at a low cost. This facilitates building manipulators for very large working spaces which cannot be obtained by other robots. 2. Low inertia: Materials provide their highest strength-to-mass ratio when they are under tensile loading. Using cables, which can be only in tension, maximizes the use of material strength and therefore reduces the mass and inertia of the manipulator. Low inertia is desirable in many applications including high speed/acceleration robotics. 3. Simplicity in structure: Cables simplify the robot structure by utilizing bending flexibility as kinematic joints and reducing the fabrication cost by minimizing the machining process. 4. Reconfigurability and transportability: Winch assemblies can be simply relocated to reconfigure and adjust the workspace of a cable-driven manipulator. The ease of assembly/disassembly of these manipulators also facilitates their transportation and quick setup. 5. Fully remote actuation: Using a fully cable-driven manipulator, all the actuators and sensitive parts are located away from the end-effector and the actual working area. Such manipulators best suit harsh or hazardous environments.