K. Kurien Issac

Gaits and energetics in terrestrial legged locomotion

In spite of the sustained worldwide efforts of the last few decades, the development of mobile robots with legs is mostly restricted to laboratories. The performances of these machines are far inferior to those of legged animals. In this paper, we study the observations made by various researchers on animal locomotion. This is done with the hope that engineers trying to design and develop legged robots would find such information useful. We focus our attention on the gaits of animals and the energy they consume for locomotion.

Finite Element and Experimental Investigation of Piezoelectric Actuated Smart Shells

In the recent years, research on the use of piezoelectric actuators for shape and vibration control of structures has been gaining prominence. Analytical and finite element models have been developed to analyze structures under piezoelectric actuation, but experimental studies, particularly on curved structures, are limited. In the current study, a finite element model is developed for piezoelectric actuated shell structures, based on Ahmad’s reduced shell element. Experiments have been conducted on a number of structures like straight beams, curved beams, and shells. Finite element and experimental results have been shown to match well. Nonlinear behavior has been observed in the experiments, particularly at higher fields, and complete hysteresis loops have been presented. The finite element is then applied to the study of deformation of a typical paraboloid shell (representative antenna shell) under piezoelectric actuation. It has been shown that piezoelectric actuation can be used to induce desired deformation shapes in the antenna shell, which result in beam steering and shaping.

An Investigation Into the Use of Springs and Wing Motions to Minimize the Power Expended by a Pigeon-Sized Mechanical Bird for Steady Flight

We gratefully acknowledge support from the Army Research Office through Grant No. W911NF-05-1-0066. The first author is grateful to his parent organization, Indian Institute of Technology Bombay, for the support provided for his sabbatical.

Beam Steering and Shaping of Smart Cylindrical Antenna

Shape control of parabolic cylindrical antennas and corresponding effect on radiation pattern, using piezoelectric actuators, is investigated. A narrow, 350-mm-long aperture, parabolic cylindrical antenna of Lexan® material is chosen for analysis. Antenna deformation is analyzed using an experimentally validated piezoelectric shell finite element. Radiation pattern is calculated using physical optics. Significant steering and shaping are obtained by deforming the antenna using centrally placed actuators. Using the strategy of making the phase variation at aperture as linear as possible and adjusting the phase difference between the two halves of the antenna to be an integral multiple of 2π, very good quality is achieved for the steered and shaped beams.

A Nondifferentiable Optimization Algorithm for Constrained Minimax Linkage Function Generation

This paper describes a nondifferentiable optimization (NDO) algorithm for solving constrained minimax linkage synthesis. Use of a proper characterization of minima makes the algorithm superior to the smooth optimization algorithms for minimax linkage synthesis and the concept of following the curved ravines of the objective function makes it very effective. The results obtained are superior to some of the reported solutions and demonstrate the algorithm’s ability to consistently arrive at actual minima from widely separated starting points. The results indicate that Chebyshev’s characterization is not a necessary condition for minimax linkages, while the characterization used in the algorithm is a proper necessary condition.

Optimal steering of a paraboloid antenna using piezoelectric actuators

The use of piezoelectric actuators to modify an antenna radiation pattern has been investigated recently. In this paper, a doubly curved paraboloid antenna of Lexan® material is considered, and the optimal size, location, and field of the piezoelectric actuators are determined, for steering the radiation. The deformation induced by the piezoactuators is determined using a shell element modified for this purpose, and validated using extensive experiments on curved beams and shells with piezopatches. The genetic algorithm is used as the optimization tool. One of the contributions of this paper is a formulation of the optimization problem which reduces the computational effort significantly. A reasonable amount of steering with good beam quality is achieved.

Simulation of impact, based on an approach to detect interference

Abstract This paper describes a method for simulating impacts which occur during the motion of planar mechanisms. An interference detection method is proposed. Using this, distance between bodies can be determined during simulation, without having to solve a system of nonlinear equations. The approach is illustrated by simulating a cam–follower mechanism. Impact is modelled using nonlinear compliance at the point of contact, and friction is modelled as Coulomb’s friction. Numerical integration is partially validated using energy balance.

Degenerated shell finite element for smart structures

Piezoelectric materials are being explored for shape and vibration control. In this paper Finite Element formulation for analyzing general shell structures under the influence of piezoelectric actuators is presented. Reduced integration is carried out to overcome problem of shear locking, and integration is carried out numerically in all three directions to obtain accurate results. The FE formulation is compared with the current literature. Experiments are conducted on curved beams and experimental results are compared with the current Finite Element formulation. Non-linearity is observed at higher voltages. Typical FEA results on a doubly curved hemispherical shell are also presented.

Obstacle Avoidance and Minimum Time Control of Cranes Using Flat Outputs and Nonlinear Programming

The problem addressed here is to determine controls for moving a load along specified trajectories which avoid obstacles. It is possible to use flat outputs to determine inputs when hoist motion is present. However, when hoist is locked, the system does not appear to be differentially flat, and hence the above approach could not be used. We propose an iterative algorithm for the problem of calculating trolley motions in this case. Results for load motions requiring (a) travel and traverse of the trolley and hoist, (b) travel and hoist, and (c) travel alone, are presented. We also use flat outputs to formulate the minimum time control problem as a nonlinear programming problem, with constraints arising from limits on trolley and hoist accelerations and velocities, and positive rope tension. Solutions obtained are also presented.© 2004 ASME