Indian Institute of Technology, Jodhpur

About: Indian Institute of Technology, Jodhpur is a education organization based out in Jodhpur, India. It is known for research contribution in the topics: Computer science & Welding. The organization has 914 authors who have published 2221 publications receiving 19243 citations.

Modeling of cutting force, tool deflection, and surface error in micro-milling operation

Abstract: Micro-milling has shown great potential in producing complex miniaturized components over wide range of materials. It can also fabricate micro-products in small batches efficiently and economically. In spite of these advantages, several challenges hinder its ability to produce components with better dimensional accuracy. Among several factors, tool deflection is one of the major sources of surface error on machined parts and features. Therefore, it is necessary to develop accurate and reliable process models to analyze and improve performance of the process. This study presents a methodology to determine cutting forces and surface error in the presence of tool deflections for micro-milling operation. Tool deflections have considerable influence on instantaneous uncut chip thickness. As tool deflection alters tooth trajectories and instantaneous uncut chip thickness, the rigid cutting force model needs to be modified suitably to consider the effect of deflections. This aspect has been incorporated in the model by modifying tool center location and tooth trajectories iteratively. The convergence of an iterative algorithm determining stable chip thickness is obtained by comparing RMS deviation of average chip thickness between two successive tooth passes. The axial variation of surface error due to tool deflections is estimated using surface generation mechanism. The proposed model is implemented in the form of a computational program to predict cutting force and surface error. The results of computational model are substantiated further by conducting machining experiments. It is shown that the proposed model predicts cutting forces fairly well in the presence of tool deflections. A comparison between predicted variation of surface error and 3D images of machined surface captured using optical microscope showed good qualitative agreement in the error profiles.

Third-order exceptional point and successive switching among three states in an optical microcavity

Abstract: One of the most intriguing topological features of open systems is that they exhibit exceptional point (EP) singularities. Apart from the widely explored second-order EPs (EP2s), the exploration of higher-order EPs in any system requires more complex topology, which is still a challenge. Here, we encounter a third-order EP (EP3) with the simultaneous presence of multiple second-order EPs in a simple fabrication feasible gain-loss assisted trilayer optical microcavity. Using the scattering-matrix formalism, we study the simultaneous interactions between three successive coupled states via avoided-resonance-crossing (ARC) phenomena, and we identify two EP2s near two ARC regimes. Such an occurrence of two EP2s inside a closed two-dimensional parametric space associated with an unbalanced gain-loss profile leads to the functionality of a cube-root branch point, i.e., an EP3. Following an adiabatic variation of two control parameters around the embedded EP3 in the presence of two identified EP2s, we present a robust successive-state-conversion mechanism among three coupled states. The proposed scheme indeed opens up a unique platform to manipulate light in integrated photonic devices.

Restricted Boltzmann machine and softmax regression for fault detection and classification

Abstract: A unique technique is proposed based on restricted Boltzmann machine (RBM) and softmax regression for automated fault detection and classification using the acoustic signal generated from IC (Internal Combustion) engines. This technique uses RBM for unsupervised fault feature extraction from the frequency spectrum of the noisy acoustic signal. These extracted features are then used to reduce the dimensionality of the training and testing data vectors. These reduced dimensionality data vectors are used by softmax regression-based classifier for classification of the engine into faulty and healthy class. The proposed technique does not require any hand-engineered feature extraction, as usually done. This technique performs very well with a small number of training data. The overall performance of this technique for four different fault classes is more than 99% on the industrial IC engine data. In a typical case, with only 38 training data sets and 210 test data sets, the performance is 99.52%.

Polymer in a double well: dynamics of translocation of short chains over a barrier

Abstract: We consider the dynamics of a short chain polymer crossing over a free energy barrier in space. Adopting the continuum version of the Rouse model, we find exact expressions for the activation energy and the rate of crossing. For this model, the analysis of barrier crossing is analogous to semiclassical treatment of quantum tunnelling. Finding the saddle point for the process requires solving a Newton-like equation of motion for a fictitious particle. The analysis shows that short chains would cross the barrier as a globule. The activation free energy for this would increase linearly with the number of units N in the polymer. The saddle point for longer chains is an extended conformation, in which the chain is stretched out. The stretching out lowers the energy and hence the activation free energy is no longer linear in N. The rates in both the cases are calculated using a multidimensional approach and analytical expressions are derived, using a new formula for evaluating the infinite products. However, due to the harmonic approximation made in the derivation, the rates are found to diverge at the point where the saddle point changes over from the globule to the stretched out conformation. The reason for this is identified to be the bifurcation of the saddle to give two new saddles, and a correction formula is derived for the rate in the vicinity of this point. Numerical results using the formulae are presented. As a function of N, it is possible for the rate to have a minimum. This is due to confinement effects in the initial state.