Kinematic Analysis and Design of the HyReCRo Robot: a Serial-Parallel and Redundant Structure-Climbing Robot
Three-dimensional vertical structures such as bridges, skeletons of buildings in the construction industry, or electrical and telecommunication towers, require inspection and maintenance tasks. These tasks imply important risks for the human operators that usually perform them, such as falling from heights. A solution to this problem consists in using climbing robots for performing such dangerous tasks.
This thesis presents the kinematic analysis and design of the HyReCRo robot (Hybrid Redundant Climbing Robot), a robot designed for climbing three-dimensional metallic structures. This robot is redundant and has a hybrid architecture, since it is composed of four 2RPR-PR parallel mechanisms serially connected. The main characteristic of this robot is that it can be driven by binary actuators in order to get closer to the basic postures necessary for exploring three-dimensional structures (namely: convex and concave plane transitions), finely adjusting later the pose of its grippers by means of continuous actuation, in order to adhere its grippers to the climbed structure. This mixed binary-continuous strategy facilitates the control and movement planning of the robot, which usually are very complex tasks in structure-climbing robots. The present thesis is focused on the study of the HyReCRo robot as a continuously-actuated robot, with the purpose of using mixed actuation strategies in the future.
In the first place, this thesis presents a complete kinematic analysis of the HyReCRo robot and of the parallel mechanisms that make up its legs. Regarding the kinematic analysis of these parallel mechanisms, this thesis demonstrates that these mechanisms can enlarge their workspace by switching between different assembly modes without traversing singularities. This occurs when enclosing special isolated singularities which are fourfold solutions of the forward kinematic problem of these parallel mechanisms. Regarding the kinematic analysis of the complete HyReCRo robot, this thesis solves both its forward and inverse kinematic problems, obtaining simple parameterizations of the 4- and 5-dimensional self-motion manifolds of this robot. These kinematic analyses are performed with the help of PaRoLa, a collection of graphical simulators developed specifically in the present thesis with the purpose of facilitating the kinematic analysis of parallel robots.
The present thesis also presents the study of the workspace of the HyReCRo robot, with the purpose of designing this robot so that it can perform convex and concave plane transitions required for exploring structures. As a result of this workspace analysis, this thesis proposes two new methods for obtaining the workspace of redundant robots, like the HyReCRo robot.
The first proposed method is an improved Monte Carlo method, which is able to obtain the boundaries of the workspace much more accurately than previously existing Monte Carlo methods, requiring the same or less computation time than them. This method consists in uniformly growing the workspace by means of normal random distributions, until the boundaries of the workspace are attained.
The second method proposed in this thesis is a method for obtaining the boundaries and interior barriers of the workspace of redundant robots induced by general collision constraints, which are difficult to obtain using previously existing methods due to their difficulties to handle such collision constraints. The proposed method identifies the vanishing of self-motion manifolds of the robot with the occurrence of interior barriers, and it consists of three stages. First, these self-motion manifolds are densely sampled, discarding samples that do not satisfy collision constraints. Next, non-discarded samples are clustered using kd-trees, with the purpose of identifying disjoint components of these manifolds. Finally, the disjoint manifolds identified at pairs of neighboring points of the workspace are compared, in order to determine if any of these manifolds vanishes when traveling from one point to its neighbor. The application of this method demonstrates that collision constraints drastically alter the distribution of interior barriers within the workspace.
Finally, this thesis concludes with the development of a totally functional prototype of the HyReCRo robot. This prototype, which weighs 2.19 kg, uses magnetic grippers based on the technology of switchable permanent magnets, achieving an adhesion force of 33 kg per gripper. This prototype has been successfully validated on real steel structures.