Mechanical Synthesis for Easy and Fast Operation in Climbing and Walking Robots

Abstract

Two different designs have been presented that contribute new approaches towards existing mechanical schemes. The first prototype is a stair-climbing wheelchair designed with a new approach, based on splitting the stair-climbing process into two sub-problems: the ascent of each single step, and the positioning of the rear and front axles. Each sub-problem is solved by using two independent mechanisms which are linked to create the final wheelchair. This new wheelchair has been modeled, built and tested. Its main features are: a) The ability to climb any staircase built according to international standards. b) Very high capacity load and weight ratio. c) Stable equilibrium is guaranteed. The second prototype consists in a new design for a leg to be used in legged or hybrid robots. The characteristics pursued and the advantages of the proposed structure are the following: The horizontal and vertical movement of the support point are decoupled, at least when in contact with the ground. The control task is very simple, with only two vertical movement commands and three horizontal movement commands per step and leg being necessary. The low number of movement commands leads to a high speed and high efficiency performance. The legged structure allows the robot to overcome obstacles, although in this case the control is not so direct, and the movements are not so fast and efficient, owing to the fact that the trajectory must be imposed not only during the traction but also during the flight stage. The motors and actuators can be independently selected for the vertical and horizontal movements, which allows the designer to select the gearboxes in order to achieve a higher speed for the horizontal movement and the load capacity for the vertical movement, without increasing the actuator capacity, and therefore without increasing its volume, height or price. A torque control rather than a speed control can be accomplished which facilitates the synchronization between the legs and smoothes the movements. In the case of both designs, the authors wish to point out the importance of a suitable mechanical scheme, fitted to the problem to be solved, in the global design of a robot. This allows the system to increase its efficiency and performance, discharging the unit control for an unnecessary task.