Eniko T Enikov

Abstract:

A continuum mechanical model of Nafion based metal-polymer actuators is presented. Global integral postulates are written for the conservation of mass, momentum, energy, and charge, Gauss' law, and the second law of thermodynamics. The global equations are then localized in the volume and on the material surfaces bounding the polymer. A finite element formulation is used to predict the evolution of the counter ion concentration, 'free' water content, electric potential, and stress/strain during actuation. The model includes stress relaxation phenomena due to water flow governed by Darcy's law.

Abstract:

There is a growing need for multi-axis force torque (F/T) sensors to aid in the assembly of micro-scale devices. Many current generation robotic microassembly systems lack the force-feedback needed to facilitate automating common assembly tasks, such as peg-in-hole insertions. Currently, most microassembly operations use vision systems to align components being assembled. However, it is difficult to view high aspect ratio component assemblies under high magnification due to the resulting limited depth-of-field. In addition, this difficulty is compounded as assembly tolerances approach dimensions resolvable with optics or if the mating parts are delicate. This paper describes the development of a high sensitivity F/T sensor. Optimal design theory was applied to determine the configuration that would result in the most sensitive and accurate sensor: Calibration experiments demonstrated that the sensor can resolve down to 200μN and possibly less. Copyright © 2005 by ASME.

Abstract:

The objective of this work is to identify design parameters for a capacitive sensor designed to recognize and record helicopter harsh landing events. Harsh landing events are typically associated with landing speeds exceeding 2.5 m/s [1] and require mandatory structural inspection resulting in down-times that could last a week or longer. In cases where no visible damage occurs, harsh-landing events might be difficult to identify and record. This paper presents a finite element analysis of the acceleration profile at different locations of the skid of a Bell 206 L4 helicopter which is then used to design and test a low-cost capacitive sensor for monitoring harsh landing events. Time history and histograms of the acceleration signal during normal and harsh landings are presented. The capacitive accelerometer is designed to operate in the 10g to 360g range. The sensor is integrated directly on a wiring board and is readout by a micro-controller with a capacitive ASIC. Details of the sensor design, fabrication, and testing are presented. The presented material also provides hard-to-find design data on the structural accelerations which can occur during harsh landing. © 2011 IEEE.

Abstract:

This article describes the experimental and numerical analysis of a novel trans-scleral tonometer based on the use of an instrumented form of digital palpation tonometry. Similar to manual digital palpation tonometery (estimation of the eye pressure via tactile touch), the novel ocular tactile tonometer utilizes multiple force probes to gather force data from indentation experiments. The presented experimental and numerical analysis shows that force data obtained from these probes correlate with the intraocular pressure (IOP) of the eye. Enucleated porcine eyes were used to validate the approach. The observed hysteresis in the force data was analyzed using an analytical model that accounts for the outflow of the aqueous humor as well as experiments at different indentation rates. Experimental data from eye distention and indentation tests were then used to infer the conditions under which the novel tonometer would be expected to have an accuracy of 1 mmHg. Analysis of the data shows that visco-elastic behavior of the scleral tissue is the primary factor responsible for the observed hysteresis. Further analysis of the data shows that indentation rates should be kept below 0.5 mm/sec for a pressure range of 10-35 mmHg. A conceptual through-the-eye-lid ocular tactile tonometer based on four probes is also presented along with numerical validation of the measured response. Copyright © 2012 by ASME.

Abstract:

Novel prognostic sensors and reasoner algorithms are the core technology for detecting defects caused by accumulation of fatigue damage in electrical and mechanical systems over time. However, serious technical challenges to implementing a general health management strategy for helicopters and military aircraft still exist. For example, severe heat and vibration make it difficult to distinguish fault signatures from environmental noise. Moreover, bearing loads are very dynamic, making it difficult to distinguish subtle wear-out signatures from normal acoustic patterns. Detection can be improved by increasing the number of sensor locations, but this option is unattractive from the standpoint of added cost, weight, and data overhead of such a system. © 2011 IEEE.