Robots araña

Proceedings of the 1999 JEEE International Conference on Robotics & Automation Detroit, Michigan May 1999

Design of a Spider-Like Robot for Motion with Quasistatic Force Constraints
Shraga Shoval IE Department, Technion shraga@hi tech.technion. ac.il Elon Rimon ME Department, Technion elon@robby. echnion.ac.il t Amir Shapiro ME Department, Technion amirs@tx.technion.ac.il

Abstract: Thispaper presents a novel design of a 4legged “spider” robot capable of moving in a wide range
of two-dimensional tunnels. The spider moves a a quan sistatic manner, by stably bracing itself against the tunnel walls and moving a free lamb to a new position. The design has been strongly influenced by the recent immobilization theory of Rimon and Burdick [13, 151. The theory dictates the minimum numberof limbs such a spider can have, as well as the shape of the footpads. The class of tunnel geometries dictates other key parameters of the spider, such as limb dimensions and number of degrees of freedom of each limb. W e review the relevant components of the immobilization theory, then describe the details of the spider design. The spider will initially move under a worst-case assumption ofslippery tunnel walls, and we also describe a locomotion strategy under this assumption. The spider has been built and is currently undergoing locomotion experiments.

1 Introduction Many motion planning problems are suited for legged robots that interact with the environment in order to achieve stable locomotion. For example, surveillance of collapsed structures for survivors, inspection and testingof aircraft engine and wing interiors, and inspection of hazardous structures such as nuclear reactors, all require motion in a congested, unstructured, and complex environment. Further, in such environments the robot cannot always rely on friction, as surfaces may be wet, oily, or icy. Our goal is to develop a general purpose multi-legged mechanism that uses quasistatic motion to navigate insuch environments. In quasistatic motion, inertial effects due to moving parts are kept small relative to the forces/torques of interaction between the robot and the environment. Motion is generated by reaction forces between the robot and the environment, and the planning of a path to the goal is subject to the constraint of maintaining stable equilibrium with the environment during the motion.Spider-like and snake-like mechanisms are examples of robots that can move quasistatically in congested environments. We now mention several works in these two areas.

In prior work on spider-like mechanisms, the robot typically moves according to a set of heuristically chosen locomotion modes, or by simple local reactive control laws. While these types of motion guarantee stable behavior of eachindividual limb, they do not necessarily guarantee stability of the whole mechanism. Examples of such spider-like mechanisms are by Madhani and Dubowsky [6], Neubauer [lo], and Stone et. al. [17]. Legged locomotion in a gravitational field is related to locomotion in congested environments. Examples of works in this area are by Boissonnat [l],Hirose [4], Marhefka [7], McGeer [9], Pfeiffer[ll],Van-den-Doe1 [18], and their coworkers. However, we focus on locomotion in congested tunnel-like environments rather than legged locomotion over a terrain. Snake-like mechanisms also interact with the environment during locomotion. They are related to spider-like mechanisms, since both mechanisms brace themselves against the environment while moving free parts toward a new position. Chrikjian andBurdick [2] and Shan and Koren [16] developed snake-like mechanisms that move by locking some of their links to the ground while allowing other links to move. These workers, as well as Hirose and Morishima [5], also investigated the use of motion patterns borrowed from biological snakes. However, virtually all existing snake-like mechanisms interact with the environment via frictional contacts with...