Search

With the emergence of augmented and virtual-reality based information delivery technologies the gap between availability of communication devices for visually impaired people and sighted people is emerging. The current study describes a communication tool which provides a reading platform for visually impaired people by means of a haptic display. In this paper the development and human subject study based evaluation of an electromagnetic microactuator-array based virtual tactile display is presented. The actuator array is comprised of a 4 by 5 array of micro voice-coil actuators (tactors) providing vibrotactile stimulation on the user’s fingertip. The size and performance of the actuators is evaluated against the thresholds of human tactile perception. It is demonstrated that a 2.65 mm (diameter) × 4 mm (height) generic tactor is suitable for practical applications in dynamic tactile displays. The maximum force of the actuator was 30 mN generated at current levels of 200 mA. At a stroke of 4.5 mm, the force is reduced to 10 mN. The peak force was generated at a displacement of 1.5 mm. A total of 10 alpha-numeric symbols were displayed to the users via dynamically changing the location of the vibrating point in a predefined sequence, thus creating a tactile perception of continuous curve. Users were asked to sketch out the perceived symbols. Each subject carried out three experiments. The first experiment exposed all subjects to ten different characters. Data obtained from human subject tests suggest that users perceive most shapes accurately, however the existence of jump discontinuities in the flow of presentation of the curves lowers recognition efficiency most likely due to loss of sensation of solid reference point. Characters containing two or more discontinuous lines such as ‘X’ were more difficult to recognize in comparison to those described with a single line such as ‘P’, or ‘Z’. Analysis of the average character recognition rate from 10 volunteers concluded that any presented character was identified correctly in 7 out 10 tests. The second test included characters that were reused from the first experiment. Users had improved their character recognition performance as a consequence of repeated exposure and learning. A final set of experiments concluded that recognition of groups of characters, forming words, is the least efficient and requires further perfecting. Recommendations for improvements of the recognition rate are also included.

Electrospinning is the most widely used production method for polymer fibers formed from an electrified fluid jet. This method is very versatile, relatively inexpensive and simple. When the sufficiently high electric potential (about 20kV) is applied to the polymer solution, the electrostatic forces overcome the surface tension of the polymer and a thin liquid jet is ejected from the nozzle. However, after short straight distance of the motion of the fiber it rapidly grows into an electric charge driven bending instability and results in a 3D spiraling trajectory leading to a very random deposition on the grounded collector. This significantly reduces the positive qualities of the fiber and its use in biomechanical engineering like a production of tissue scaffolds mimicking the structure of the extracellular matrix or a delivery of expandable chemo- and radio-therapeutic stents. In this work we present the initial results from investigating the feasibility of using dynamic focusing of the electrified jet in a linear quadrupole trap. This is a new alternative to the more generally used mechanical approach with rotating mandrel, could in principle lead to the ability to control the deposition location without the use of any moving components. The proposed approach was originally developed for trapping and transporting individual charged ions. In contrast to ions, an electrified continuous fiber represents an infinite degree of freedom system, with potentially much richer dynamics and unknown stability regions in the parameter space. In order to understand the dynamics of the fiber, we present a discretized 2D reduced-order mathematical model which is investigated numerically. The resulting ODEs represent multi-dimensional form of a non-linear Mathieu’s and Meissner’s differential equations for harmonic, and step excitation functions, respectively. The model parameters were obtained from static experiments with electrodes compressing the fibers in a single plane. Finite-element model of the electrodes resulted in detailed potential maps, which were used to develop estimates of the required strength of the electrostatic field needed to steer the fibers. The estimated parameters were used to obtain stable solutions of the reduced-order approximate of a spring-mass-charged dumbbell model of the fiber.

This paper describes the development of a highly sensitive microfluidics flow sensor using MTJ magnetic sensors to detect motion of slow-moving fluids. A motivating application for the proposed device is the development of an implantable flow sensor, capable of monitoring the amount of cerebral spinal fluid drained from the ventricles of the brain. Micro-fabricated ferromagnetic flaps are used to detect motion of the surrounding fluid. The deflection of the flaps is detected by an ultra-sensitive MTJ magnetic field sensor placed outside of the lumen of the catheter. Previous studies have presented a working device with a resolution of up to 1.4 mL/hr. This paper presents the improvements made to the device in terms of sensitivity, thermal noise rejection, and dynamic response. Upon investigation of possible noise sources, a thermally induced sensor drift was found to be the most significant factor affecting the sensors response. A static temperature compensation reduced this drift to less than 120 mL per 12-hr period. Further improvements to the design of the ferromagnetic transducers resulted in a 4.5-fold increase in sensitivity over the previous designs. Results from dynamic testing of the sensor revealed a time constant of 0.4 seconds, which was found adequate for the envisioned application.Copyright © 2016 by ASME

The objective of this National Science Foundation (NSF)-funded undergraduate engineering training project is to introduce nanoscale science and engineering through an innovative use of a technical elective sophomore-level mechatronics course, followed by an Accreditation Board for Engineering and Technology (ABET)-mandated senior-level engineering capstone design project. A unique partnership between University of Arizona’s department of surgery, its neurosurgical division, and the College of Engineering presents a creative environment, where medical residents serve as mentors for undergraduate engineering students in developing product ideas enabled by nanotechnology. Examples include: a smart ventricular peritoneal (VP) shunt with flow-sensing; a bio-resorbable inflatable stent for drug delivery, and a hand-held non-invasive eye tonometer. Results from the first year of the student projects, as well as qualitative assessment of their experience, is presented. Several institutional challenges were also identified.Copyright © 2015 by ASME

This article presents the early results from a 10-person human subject study evaluating the accuracy of a novel method of indirect estimation of intraocular pressure using tactile sensors. Manual digital palpation tonometery is an old method used to estimate the eye pressure through palpation with ones fingers. Based on this concept, we present an instrumented measurement method, where multiple tactile stiffness sensors are used to infer the intraocular pressure of the eye. The method is validated using experimental data gathered from human subjects with eye pressures from 15 to 22 mmHg and determined by Goldman applanation tonometry (GAT). Bland-Altman plots comparing the GAT measurements and the proposed through-the-eye-lid tonometry indicate a statistical error of 5.16 mmHg, within the 95% confidence interval, which compares favorably with the FDA-mandated error bound of 5 mmHg. Details on the unit operation and data filtering are also presented. Due to its indirect and non-invasive nature, the proposed new tactile tonometry method can be applied at home as a self-administered home tonometer for management of glaucoma.Copyright © 2015 by ASME

Central retinal vein occlusion (CRVO) is a vascular disease characterized by thrombosis of the retinal veins that can eventually lead to ischemia. Ischemic CRVO can then cause macular degeneration and neovascular glaucoma causing partial to full blindness. In this study, we determined the feasibility of electrospinning tubular scaffolds for treating CRVO and vascular disease. Electrospinning was utilized to produce customizable scaffolds from nano-bers using collagen type I. Scaffolds were treated with glutaraldehyde, glycine, ethanol, UV light, and combinations of the treatments for the purpose cross-linking and to study their angiogenic effects. Structural properties of the scaffolds were analyzed with scanning electron micrsoscopy (SEM). Scaffolds were immobilized with human recombinant vascular endothelial growth factor (rhVEGF165) to investigate the drug-delivering abilities of the electrospun materials and as a method to produce vascularization. The chick chorioallantoic membrane (CAM) assay was used to examine the effects of VEGF immobilizations and to evaluate the feasibility of creating an anastomosis to treat CRVO. Collagen onplants (non-electrospun) and electrospun implants were made on day 10 of embryonic development. Findings show collagen loaded with rhVEGF165 had improved vasculature and pro-angiogenic properties. The present study suggests that collagen can immobilize and release growth factor, be electrospun to mimic the ultrastructure of native blood vessels, and holds promise for vascular tissue engineering.Copyright © 2013 by ASME

Thermo-tunneling of hot electrons across a few nanometer gap has application to vacuum electronics, flat panel displays, and holds great potential in thermo-electric cooling and energy generation. However development of such applications requires formation of dynamically balanced gap separating the two surfaces. One such approach is the use of Lorentz (repulsive) and Coulomb (attractive) forces to obtain an equilibrium gap between two elastic electrodes. The present paper describes the application of the Differential Quadrature Method (DQM) to the solution of a clamped-clamped Euler-Bernouli beam subject to the combined action of Lorentz and Coulomb forces. The results show that due to non-local action of the Lorentz force, the shape of the tunneling electrode is inherently non-uniform with Coulomb forces acting primarily at one end of the beam while the Lorentz force distributed along the remaining part. DQM method also allows analysis of the stability of the tunneling current as a function of the applied external potential and magnetic field. In addition to the classical electrostatic pull-in instability with no-tunneling, a second regime with non-zero tunneling current is also identified. To the best of our knowledge this is the first attempt to analyze this phenomenon under the effect of both Electrostatic and Lorenz forces in this particular case. Linear stability analysis of the tunneling regime indicates the appearance of a saddle-saddle bifurcation indicating unstable tunneling regime.

This article describes a novel method of indirect estimation of intra-ocular pressure using tactile sensors. Two sensor calibration methods have been demonstrated: an artificial neural network (ANN) model and a phenomenological reduced-parameter model based on finite element analysis. The ANN method showed superior performance with an accuracy of +/− 0.7 mmHg, while the reduced order method showed an accuracy of +/− 3.11 mmHg. The latter method however allows calibration of the tactile tonometer from a single pressure measurement if the geometry of the probes is known and satisfying certain solvability conditions. The ANN method was demonstrated using experiment data, while the reduced-order model was tested numerically. Due to its indirect and non-invasive nature, the proposed tactile measurement method can be used in the development of a self-administered home tonometer for management of glaucoma, however the presence of an eye lid might require modification of the calibration procedure outlined here.Copyright © 2013 by ASME

Teaching classical controls systems design to mechanical engineering students presents unique challenges. While most mechanical engineering programs prepare students to be well-versed in the application of physical principles and modeling aspects of physical systems, implementation of closed loop control and system-level analysis is lagging. It is not uncommon that students report difficulty in conceptualizing even common controls systems terms such as steady-state error and disturbance rejection. Typically, most courses focus on the theoretical analysis and modeling, but students are left asking the questions…How do I implement a phase-lead compensator? …What is a non-minimum phase system? This paper presents an innovative approach in teaching control systems design course based on the use of a low-cost apparatus that has the ability to directly communicate with MATLAB and its Simulink toolbox, allowing students to drag-and-drop controllers and immediately test their effect on the response of the physical plant. The setup consists of a DC micro-motor driving a propeller attached to a carbon-fiber rod. The angular displacement of the rod is measured with an analog potentiometer, which acts as the pivot point for the carbon fiber rod. The miniature circuit board is powered by the USB port of a laptop and communicates to the host computer using the a virtual COM port. MATLAB/Simulink communicates to the board using its serial port read/write blocks to command the motor and detect the deflection angle. This presentation describes a typical semester-long experimental protocol facilitated by the low-cost kit. The kit allows demonstration of classical PID, phase lead and lag controllers, as well as non-linear feedback linearization techniques. Comparison between student gains before and after the introduction of the mechatronic kits are also provided.Copyright © 2012 by ASME

Combined thermionic emission and tunneling of hot electrons (thermo-tunneling) has emerged as a potential new solidstate cooling technology. Practical implementation of thermo-tunneling, however, requires the formation of a nanometer-sized gap spanning macroscopically significant surfaces. Thermo-tunneling is a term used to describe combined emission of hot electrons (thermionic emission) and tunneling of electrons through a narrow potential barrier between two surfaces (field emission). Thermo-tunneling of hot electrons across a few-nanometer gap has application to vacuum electronics, flat panel displays, and holds great potential in thermo-electric cooling and energy generation. Development of new thermo-tunneling applications requires creation of a stable nanometer gap between two surfaces. This presentation is focused on our effort to investigate the stability of the the thin flexible structure under electrostatic and lorenz forces opposing each other. In this presentation, we report the result of numerical simulation with some mathematical simplifications. The mathematical model used for the numerical simulation is well studied in the literature. Using forth-order partial differential beam equation, we studied the steady state solutions of the thermo-tunneling beam model using Galerkin method. Essential output parameters of the model include a central contact area measured by its length (delta) and the thermo-tunneling current. Both parameters are determined as a function of the externally applied external potential and magnetic field. Numerical solutions of the model show two possible operating modes: (1) symmetric deformation with negligibly small current; and (2) asymmetric mode where the B-field controls the current and contact area. Under practical values for the externally applied magnetic and electric fields, it has been shown that the second mode is only possible for electrode with very low work functions, e.g. below 0.5 eV. Therefore, novel materials such as Diamond-like carbon films are likely to be essential in thermo-tunneling applications.

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

A gas or vapor compressor is one of the key components of many engineering systems, such as certain designs of vapor compression refrigeration systems, cryo-coolers, air handlers. For meso-scale systems with linear dimensions of a few centimeters, conventional designs do not work efficiently because of rather large relative tolerances, and hence these meso-scale systems require micro-fabricated components for efficient operation. This paper presents a meso-scale centrifugal compressor fabricated by photo-lithographic techniques. A preliminary design based on 1-D flow analysis using air as the working fluid shows that a 50 mm diameter centrifugal compressor with a blade height of 200 μm gives a static pressure ratio of 1.12. In this design, the impeller has 10 full blades and 10 splitter blades. Each blade has the NACA profile 9510 with the maximum camber at 50% of the chord. These impeller blades have exit angles 35° with exit flow angles of 60°. A vaned diffuser having 20 equally spaced vanes with the same NACA profile is used to improve compressor efficiency. A 3-D compressible, viscous flow analysis has been done using a commercial finite volume software. The results of this analysis allowed the verification of the flow characteristics inside the meso-scale centrifugal compressor. The compressor has been fabricated using micro-fabrication techniques. The rotor and the stator are made by etching a silicon wafer by using DRIE (Deep Reactive Ion Etching) technique. A Pyrex wafer is then bonded to the stator for visual access inside the compressor.

In this paper we present results of our task of assembly of hybrid magnetic MEMS devices. The contact phase of assembly for MEMS devices is complicated by the presence of surface effect and magnetic forces. This forces a path planning strategy that accounts for the mechanics of part interactions at such scales for all contact phases in order to guarantee successful and repeatable assemblies. To validate and demonstrate the applicability of microassembly strategies, we have developed a flexible automated microassembly workcell with integrated part handling skills which is also described.