Using Parallel Platforms as Climbing Robots

Abstract

Primates are the living beings with a greater capacity of manipulation. This skill derives from they have two legs equipped with elements adapted to the manipulation and grasping. The simultaneous use of both legs and arms confer to these living beings their special features to manipulate and manage different objects. As many technical developments inspired when nature laws are observed, parallel robots are conceived in a similar way. In this way, the mechanical structure of a parallel robot is composed by a closed chain in which the end effector is linked to the basis at least by two independent kinematic chains.This definition can be in conflict with the developments about coordinated robots that also constitute closed kinematic chains. Parallel robots simplify these chains in such a way that every one has only one actuator. So, the complexity of the mechanism can be reduced and it is possible to make good use of the energy provided by the actuators to obtain a higher payload capacity or to increase the speed of movement of the end effector. The first theoretical works on mechanical parallel structures appear long time ago, even before the notion of robot. In this way the first parallel mechanism was patented in 1931 (US Patent No 1789680) and was designed by James E. Gwinnett (Gwinnett 1931). In 1940 Willard Pollard presented a robot with 5 degrees of freedom dedicated to painting tasks. The robot was composed of three legs of two links each one. The three actuators of the base drive the position of the tool.However, other more significant parallel mechanisms have been achieved from then. In this way, in 1947 Eric Gough designed the most popular parallel platform. Nowadays numerous platforms can be found with the name of MAST (Multi-Axis Simulation Table). In 1965, Mr. Stewart (Stewart, 1965) described a movement platform of 6 degrees of freedom (dof) designed to use as a flight simulator. On the contrary to the general belief the Stewart mechanism is different to the previously presented by Gough. The work presented by Stewart had and have a great influence in the academic world, and it is considered one of the first works of analysis of parallel structures. At the same time, Klaus Cappel carried out in the Franklin Institute Research Laboratory a lot of researches with parallel platforms of 6 degrees of freedom. In 1967 Cappel patented a motion simulator based on a hexapod (Cappel, 1967). Later, in 1978 Hunt (Hunt 1978) suggested that the mechanisms of the flight simulators can be used as parallel robots. Also Hunt pointed out that parallel robots required a more detailed study in the context of robotic applications due to the advantages of accuracy and rigidity of these platforms.