Bishakh Bhattacharya

Pseudo-rigid Body Modeling of IPMC for a Partially Compliant Four-bar Mechanism for Work Volume Generation

Conventional four-bar crank rocker mechanisms made of rigid links can generate only one path, at the rocker tip, for one revolution of the crank. However, if the rocker length can be actively changed then its tip can generate a work volume. This study describes an application of ionic polymer metal composite (IPMC) as a partially compliant rocker in a four-bar mechanism for work volume generation. First, an experiment is conducted to study the voltage verses bending characteristics of IPMC and based on the experimental data the IPMC is modeled using a pseudo rigid body model. The model is based on the fix-pin support type of cantilever mode and its derivation is explained in detail. The maximum and minimum length of the rocker is controlled by changing the voltage applied to it and this generates a work volume for one revolution of the crank. Simulation results are compared with the experimentally obtained work volume and the differences are found. The proposed mechanism has the potential for application in micro positioning, compliant structures, etc.

Multi-Objective Optimization of Piezoelectric Actuator Placement for Shape Control of Plates Using Genetic Algorithms

Shape control of adaptive structures using piezoelectric actuators has found a wide range of applications in recent years. In this paper, the problem of finding optimal distribution of piezoelectric actuators and corresponding actuation voltages for static shape control of a plate is formulated as a multi-objective optimization problem. The two conflicting objectives considered are minimization of input control energy and minimization of mean square deviation between the desired and actuated shapes with constraints on the maximum number of actuators and maximum induced stresses. A shear lag model of the smart plate structure is created, and the optimization problem is solved using an evolutionary multi-objective optimization algorithm: nondominated sorting genetic algorithm-II. Pareto-optimal solutions are obtained for different case studies. Further, the obtained solutions are verified by comparing them with the single-objective optimization solutions. Attainment surface based performance evaluation of the proposed optimization algorithm has been carried out.

Active Vibration Control Strategy for a Single-Link Flexible Manipulator Using Ionic Polymer Metal Composite

Ionic polymer metal composites (IPMC) are a class of electro-active polymers (EAP) that produce mechanical strain in response to electrical stimulation and vice versa. The property of generating high strains with low actuation voltage makes IPMC suitable for mechanical actuators in applications involving control of high-amplitude vibration. This article describes results on an application of IPMC as an active damper for large deflection vibration control of a single link rotating flexible manipulator. Modeling of the flexible rotating link has been done using modal approach and it was found that the first two modes of vibration take the maximum amount of energy. Based on this, two IPMC actuators were fixed at suitable positions on the link to suppress vibrations. A dynamic model of the link with IPMC was derived and a distributed PD controller designed to actuate the IPMC to control the vibration of the flexible link. Simulations were first done to demonstrate the effectiveness of IPMC and then experiments are conducted to validate the results. The results prove that IPMC can be used as an active damper for suppressing vibration in a flexible link manipulator.

Active and passive vibration control of flexible structures using a combination of magnetostrictive and ferromagnetic alloys

A combined passive and active damping strategy is proposed to control vibration in structures using a combination of layers of ferro-magnetic (passive) damping and smart (active) magnetostrictive material (Terfenol-D). Two types of combined damping systems are considered viz., a noninteractive system and an interactive or hybrid system. Numerical investigations on a cantilever beam model are carried out to investigate various aspects in combined damping scenario. Using variational principle, a beam Finite Element is developed to study the dynamic characteristics of a beam containing both the passive and active damping layers. It is shown that the combined system could be used effectively to dampen the structural vibration over a wide frequency range. Comparisons with only passive and only active damping schemes are also made. The influence and the mode dependence of control gain in a hybrid system is clearly brought out.

Analysis and control of friction-induced oscillations in a continuous system

We analyse and control friction-induced oscillations in a continuous system due to the drooping characteristics of the friction force. The model consists of a cantilever beam with an end mass that is in frictional contact with a rigid rotating disc. Time-delayed displacement feedback applied normal to the disc surface is used to control the vibrations. Linear stability analysis yields the stability boundary corresponding to the Hopf bifurcation point. Nonlinear analysis is performed to obtain conditions on the control parameters for which the nature of the bifurcation is subcritical such that these values can be avoided. The control parameters for effective quenching of the vibrations are obtained. An interesting regime of control parameters for which the system is stable for low and high velocities but unstable for intermediate velocities is also observed.

An active vibration control strategy for a flexible link using distributed ionic polymer metal composites

Ionic polymer metal composites are a class of electro-active polymers that are gaining importance as smart actuators due to their large bending deflection. The property of generating high strains with low actuation voltage makes ionic polymer metal composites (IPMC) suitable for applications requiring large motion such as in large deflection vibration suppression. In this paper we propose an application of IPMC as an active damper for large deflection vibration control of a flexible link. The modes of vibration for a long flexible link are derived using the modal approach and two IPMC patches are placed to suppress the vibration. A distributed PD controller is designed to suppress the vibration of the flexible link for the desired positioning of the tip. Simulations are first done to demonstrate effective vibration suppression and the results proved that the proposed method can suppress vibration effectively. Experiments are conducted to verify the application of IPMC for active vibration suppression. The performance of the proposed distributed PD controller is also found to be better than a single PD controller loop.

Active Vibration Suppression of a Flexible Link Using Ionic Polymer Metal Composite

Polymers labeled as EAPs (electro-active polymer) have a mechanical response to electrical stimulation and produce an electric change in response to mechanical stimulation. The high strains of ionic polymer metal composite (IPMC) make them attractive as mechanical actuators for applications requiring large motion but little force. This paper describes the results an application of IPMC as active damper for a flexible link. IPMC is studied experimentally to find out material loss factors and damping characteristics. A single link rotary flexible manipulator with IPMC as smart patches was studied for attenuation of vibration actively. Modeling of the flexible rotating beam with IPMC has been done using modal approach to determine the fundamental modes of vibration. The end effector position of link was controlled by generating localized bending by giving input current to the IPMC in a phase opposite to the excitation. The results prove that IPMC can be used as an active damper for suppressing vibration in a flexible link

Analysis and Design Optimization of a Robotic Gripper Using Multiobjective Genetic Algorithm

Robot gripper design is an active research area due to its wide spread applicability in automation, especially for high-precision micro-machining. This paper deals with a multiobjective optimization problem which is nonlinear, multimodal, and originally formulated. The previous work, however, had treated the actuator as a blackbox. The system model has been modified by integrating an actuator model into the robotic gripper problem. A generic actuation system (for example, a voice coil actuator) which generates force proportional to the applied voltage is considered. The actuating system is modeled as a stack consisting of the individual actuator elements arranged in series and parallel arrays in four different combinations. With the incorporation of voltage into the problem, which is related to both actuator force and manipulator displacement, the problem becomes more realistic and can be integrated with many real-life gripper simulations. Multiobjective evolutionary algorithm is used to solve the modified biobjective problem and to optimally find the dimensions of links and the joint angle of a robot gripper. A force voltage relationship can be obtained from each of the nondominated solutions which helps the user to determine the voltage to be applied depending on the application. An innovization study is further carried out to find suitable relationships between the decision variables and the objective functions.

Variation of activation volume with temperature for Fe, Si, and Ge

In this paper, a new approach is presented to calculate the activation volume, which is based on Eyring absolute reaction rate theory. Emphasis is placed on the determination of activation volume from the indentation creep microhardness data measured using Vickers indentor at constant load for various dwell times and temperatures. Different materials like Fe (with metallic bonding), Si, and Ge (with covalent bonding) are chosen for the study. The results serve to validate the approach outlined here because direct comparison can be made with the data obtained through a conventional creep test of specimens. The result obtained also shows that activation volume increases with increasing homologous temperature.

Design of a vibration isolation system using eddy current damper

This article aims at modeling, analysis and design of a passive vibration isolation system using a magnetic damper with high efficiency and compactness. The experimental set-up was developed for a single degree-of-freedom vibration isolation system, where the damper consists of two elements: an outer stationary conducting tube made up of copper and a moving core made up of an array of three ring-shaped neodymium magnets of Nd–Fe–B alloy separated by four block cylinders made of mild steel that are fixed to a steel rod. The generation of eddy currents in the conductor and its resistance causes the mechanical vibration to dissipate heat energy. The vibration response of the system is obtained starting from a low-frequency range. The proposed magnetic damper achieves a maximum transmissibility value less than two for a natural frequency that is less than 10 Hz and the excitations at higher frequencies are successfully isolated. Numerical and experimental studies were carried out for a range of system parameters which show that isolators based on magnetic damping could be very effective for passive vibration isolation. Further, a theoretical model for an active isolation system is proposed in order to reduce the transmissibility at resonance. It is envisaged that the combined active–passive eddy current damper could be effectively used for vibration isolation.