Showing papers by "Asokan Thondiyath published in 2011"

Combinational scissor-grasper tool for use in laparoscopy

Abstract: Disclosed is a four-jawed combinational scissor-grasper surgical tool for use in laparoscopy. Cutting and grasping functionalities are respectively enabled via movement of a pair of such specially contoured jaw members sliding against or splaying apart from the other pair. Also disclosed are means for achieving selectable interlocking of jaw members and mechanical linkage for their actuation by human user.

A non-linear tracking control scheme for an under-actuated autonomous underwater robotic vehicle †

Abstract: This paper proposes a model based trajectory tracking control scheme for under-actuated underwater robotic vehicles. The difficulty in stabilizing a non-linear system using smooth static state feedback law means that the design of a feedback controller for an under-actuated system is somewhat challenging. A necessary condition for the asymptotic stability of an under-actuated vehicle about a single equilibrium is that its gravitational field has nonzero elements corresponding to non-actuated dynamics. To overcome this condition, we propose a continuous time-varying control law based on the direct estimation of vehicle dynamic variables such as inertia, damping and Coriolis & centripetal terms. This can work satisfactorily under commonly encountered uncertainties such as an ocean current and parameter variations. The proposed control law cancels the non-linearities in the vehicle dynamics by introducing non-linear elements in the input side. Knowledge of the bounds on uncertain terms is not required and it is conceptually simple and easy to implement. The controller parameter values are designed using the Taguchi robust design approach and the control law is verified analytically to be robust under uncertainties, including external disturbances and current. A comparison of the controller performance with that of a linear proportional-integral-derivative (PID) controller and sliding mode controller are also provided.

An Improved Algorithm for Constrained Multirobot Task Allocation in Cooperative Robot Tasks

Abstract: This paper presents an improved algorithm for solving the complex task allocation problem in constrained multiple robot cooperative tasks. The existing multiple robot task allocation mechanisms do not discuss much about complex tasks, instead they treat tasks as simple, indivisible entities. Complex tasks are tasks that can be decomposed into a set of subtasks and so can be executed by several possible ways. The goal of cooperative task allocation algorithm for multiple mobile robots is to find which robot should execute which task in order to maximize the global efficiency and minimize the cost. Some factors such as benefit, cost, resources, and time should be considered during the course of task allocation. The meta-heuristic algorithm proposed here solves the task allocation problems with the characteristics like each task requires a certain amount of resources and each robot has a finite capacity of resource to be shared between the tasks it is assigned. The cost of solution which includes static costs when using robots, assignment cost, and communication cost between the tasks if they are assigned to different robots are also taken into account in developing the solution. A peer search scheme algorithm for solving the constrained task allocation problem is presented. Computational experiments using this algorithm have shown that the proposed method is superior in terms of computation time and solution quality.