Effect of Load on Machine Geometry with Respect to the Weight and Torque

RÉSUMÉ Dans cette étude, une méthode est développée pour estimer et prédire les coefficients d'erreur de la déformation d‟une machine CNC à cinq axes sous différentes conditions de chargement. Pour étudier l'effet de différents poids et les couples sur les erreurs de la machine, les blocs lourds identiques (10 kg chacun) ainsi que des entretoises lumière ont été conçus et fabriqués. Après installer les bocs et les boules sur la palette, la machine sonde les boules pour différents angles indexés par rapport à ses deux axes de rotation (B et C axes) en utilisant les codes G générés par programme RUMBA (the 3D reconfigurable uncalibrated master balls artifact). Au total, il y a 26 types d'erreurs et chaque erreur a maximum de cinq coefficients qui sont appelés coefficients d'erreur estimés. Les données obtenues à partir de la machine sont traitées afin d'estimer les valeurs des coefficients d'erreur pour chaque erreur. Ces derniers permettent d'obtenir les graphiques polynômes de chaque erreur en utilisant leurs coefficients d'erreur. En outre, la matrice de corrélation de Pearson est obtenue pour tous les coefficients d'erreur et des poids et des couples. Les éléments de la matrice de corrélation (entre -1 et 1) indiquent le degré de dépendance de chaque coefficient d'erreur pour les autres coefficients, ainsi que le poids et le couple. Enfin, le procédé d'ajustement de la courbe est utilisé pour modéliser chaque coefficient d'erreur en fonction du poids et du couple. Ceci permet de prédire la valeur du coefficient d'erreur pour toutes les valeurs de poids et de couple supprimant la nécessité l'essai expérimental. L'analyse résiduelle (la différence entre les valeurs expérimentales et les valeurs prédites) est ensuite utilisée pour vérifier l'exactitude du modèle. Les résultats de cette étude montrent que cette méthode est suffisamment précise pour estimer les erreurs de la machines qui est testés (HU40T machine CNC à cinq axes). Le modèle nous permet d'estimer les valeurs des coefficients d'erreur en fonction du poids uniquement, en fonction du couple uniquement et en fonction du poids et du couple simultanément. Cette connaissance est importante pour la compensation d'erreur ou la suppression d'erreur dans la machine pour augmenter la précision de la fabrication.----------ABSTRACT In this study, a method is developed to estimate and predict the error coefficients of a five-axis CNC machine tool deformation under different loading conditions. To study the effect of different weights and torques on the machine errors, identical heavy blocks (10 Kilograms each) as well as light spacers (less than 1 Kilogram) are designed and fabricated. After assembling the blocks and master balls on the pallet, the machine probes the balls for different indexations from the rotary axes (B and C axes) of the machine using G-codes generated from the 3D reconfigurable uncalibrated master balls artefact (RUMBA) program. In total, there are 26 types of errors and each error has maximum five coefficients which are called estimated error coefficients. The raw data obtained from machine is processed to estimate the values of the error coefficients for each error. Then, the polynomial function of each error can be achieved by using their error coefficients. Furthermore, Pearson‟s correlation matrix is obtained for all error coefficients and weights and torques. The elements of the correlation matrix (between -1 and 1) show the extent of dependency of each error coefficient to other coefficients as well as to the weight and torque. Finally, the curve fitting method is used to model each error coefficient as a function of weight and torque. The modeling allows predicting the value of the error coefficient for any weights and torques without doing an experimental test. Residual analysis (difference between the experimental and the predicted values) is then used to verify the accuracy of the modeling. The results of this study show that this method is accurate enough to estimate the errors of the tested machine tool (HU40T 5-axis CNC machine tools). The model enables us to estimate the error coefficient values as a function of weight independently, torque independently and weight and torque simultaneously. This knowledge is important for error compensation or even error removal in machine to increase the precision of the manufacturing

A Subdomain Method for Mapping the Heterogeneous Mechanical Properties of the Human Posterior Sclera

Although strongly correlated with elevated intraocular pressure, primary open-angle glaucoma (POAG) occurs in normotensive eyes. Mechanical properties of the sclera around the optic nerve head (ONH) may play a role in this disparity. The purpose of this study is to present an automated inverse mechanics based approach to determine the distribution of heterogeneous mechanical properties of the human sclera as derived from its surface deformations arising from pressure in fl ation experiments. The scleral shell of a 78 year old European Descent male donor eye was utilized to demonstrate the method; the sclera was coated with a speckle pattern on the outer surface and was subjected to in fl ation pressures of 5, 15, 30, and 45 mmHg. The speckle pattern was imaged at each pressure, and a displacement fi eld was calculated for each pressure step using a previously described sequential digital image correlation(S-DIC) technique. The fiber splay and fiber orientation of the sclera collagen were determined experimentally, and the thickness across the scleral globe was determined using micro CT images. The displacement fi eld from the in fl ation test was used to calculate the strain and also used as an input for inverse mechanics to determine the heterogeneity of material properties. The scleral geometry was divided into subdomains using the first principal strain. The Holzapfel anisotropic material parameters of matrix and fiber stiffness were estimated within each individual subdomain using an inverse mechanics approach by minimizing the sum of the square of the residuals between the computational and experimental displacement fields. The mean and maximum error in displacement across all subdomains were 8.9 +/- 3.0 mu m and 13.2 mu m, respectively. The full pressure-inflation forwardmechanics experiment was done using subdomain-specific mechanical properties on the entire scleral surface. The proposed approach is effective in determining the distribution of heterogeneous mechanical properties of the human sclera in a user-independent manner. Our research group is currently utilizing this approach to better elucidate how scleral stiffness influences those at high risk for POAG.National Eye Institute of the National Institutes of Health (NIH) [R01EY020890, R01FD006582]; University of Pittsburgh Center for Research Computing (CRC); Pittsburgh Supercomputer Center through NSF-XSEDE award [TG-ENG160035]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Effective swimming strategies in low Reynolds number flows

The optimal strategy for a microscopic swimmer to migrate across a linear shear flow is discussed. The two cases, in which the swimmer is located at large distance, and in the proximity of a solid wall, are taken into account. It is shown that migration can be achieved by means of a combination of sailing through the flow and swimming, where the swimming strokes are induced by the external flow without need of internal energy sources or external drives. The structural dynamics required for the swimmer to move in the desired direction is discussed and two simple models, based respectively on the presence of an elastic structure, and on an orientation dependent friction, to control the deformations induced by the external flow, are analyzed. In all cases, the deformation sequence is a generalization of the tank-treading motion regimes observed in vesicles in shear flows. Analytic expressions for the migration velocity as a function of the deformation pattern and amplitude are provided. The effects of thermal fluctuations on propulsion have been discussed and the possibility that noise be exploited to overcome the limitations imposed on the microswimmer by the scallop theorem have been discussed.Comment: 14 pages, 5 figure

Biohybrid microtube swimmers driven by single captured bacteria

Bacteria biohybrids employ the motility and power of swimming bacteria to carry and maneuver microscale particles. They have the potential to perform microdrug and cargo delivery in vivo, but have been limited by poor design, reduced swimming capabilities, and impeded functionality. To address these challenge, motile Escherichia coli are captured inside electropolymerized microtubes, exhibiting the first report of a bacteria microswimmer that does not utilize a spherical particle chassis. Single bacterium becomes partially trapped within the tube and becomes a bioengine to push the microtube though biological media. Microtubes are modified with "smart" material properties for motion control, including a bacteria-attractant polydopamine inner layer, addition of magnetic components for external guidance, and a biochemical kill trigger to cease bacterium swimming on demand. Swimming dynamics of the bacteria biohybrid are quantified by comparing "length of protrusion" of bacteria from the microtubes with respect to changes in angular autocorrelation and swimmer mean squared displacement. The multifunctional microtubular swimmers present a new generation of biocompatible micromotors toward future microbiorobots and minimally invasive medical applications

Acoustic Communication for Medical Nanorobots

Communication among microscopic robots (nanorobots) can coordinate their activities for biomedical tasks. The feasibility of in vivo ultrasonic communication is evaluated for micron-size robots broadcasting into various types of tissues. Frequencies between 10MHz and 300MHz give the best tradeoff between efficient acoustic generation and attenuation for communication over distances of about 100 microns. Based on these results, we find power available from ambient oxygen and glucose in the bloodstream can readily support communication rates of about 10,000 bits/second between micron-sized robots. We discuss techniques, such as directional acoustic beams, that can increase this rate. The acoustic pressure fields enabling this communication are unlikely to damage nearby tissue, and short bursts at considerably higher power could be of therapeutic use.Comment: added discussion of communication channel capacity in section

Chemical Power for Microscopic Robots in Capillaries

The power available to microscopic robots (nanorobots) that oxidize bloodstream glucose while aggregated in circumferential rings on capillary walls is evaluated with a numerical model using axial symmetry and time-averaged release of oxygen from passing red blood cells. Robots about one micron in size can produce up to several tens of picowatts, in steady-state, if they fully use oxygen reaching their surface from the blood plasma. Robots with pumps and tanks for onboard oxygen storage could collect oxygen to support burst power demands two to three orders of magnitude larger. We evaluate effects of oxygen depletion and local heating on surrounding tissue. These results give the power constraints when robots rely entirely on ambient available oxygen and identify aspects of the robot design significantly affecting available power. More generally, our numerical model provides an approach to evaluating robot design choices for nanomedicine treatments in and near capillaries.Comment: 28 pages, 7 figure

A Subdomain Method for Mapping the Heterogeneous Mechanical Properties of the Human Posterior Sclera

Although strongly correlated with elevated intraocular pressure, primary open-angle glaucoma (POAG) occurs in normotensive eyes. Mechanical properties of the sclera around the optic nerve head (ONH) may play a role in this disparity. The purpose of this study is to present an automated inverse mechanics based approach to determine the distribution of heterogeneous mechanical properties of the human sclera as derived from its surface deformations arising from pressure inflation experiments. The scleral shell of a 78 year old European Descent male donor eye was utilized to demonstrate the method; the sclera was coated with a speckle pattern on the outer surface and was subjected to inflation pressures of 5, 15, 30, and 45 mmHg. The speckle pattern was imaged at each pressure, and a displacement field was calculated for each pressure step using a previously described sequential digital image correlation (S-DIC) technique. The fiber splay and fiber orientation of the sclera collagen were determined experimentally, and the thickness across the scleral globe was determined using micro CT images. The displacement field from the inflation test was used to calculate the strain and also used as an input for inverse mechanics to determine the heterogeneity of material properties. The scleral geometry was divided into subdomains using the first principal strain. The Holzapfel anisotropic material parameters of matrix and fiber stiffness were estimated within each individual subdomain using an inverse mechanics approach by minimizing the sum of the square of the residuals between the computational and experimental displacement fields. The mean and maximum error in displacement across all subdomains were 8.9 ± 3.0 μm and 13.2 μm, respectively. The full pressure-inflation forward mechanics experiment was done using subdomain-specific mechanical properties on the entire scleral surface. The proposed approach is effective in determining the distribution of heterogeneous mechanical properties of the human sclera in a user-independent manner. Our research group is currently utilizing this approach to better elucidate how scleral stiffness influences those at high risk for POAG

Applications of molecular communications to medicine: A survey

In recent years, progresses in nanotechnology have established the foundations for implementing nanomachines capable of carrying out simple but significant tasks. Under this stimulus, researchers have been proposing various solutions for realizing nanoscale communications, considering both electromagnetic and biological communications. Their aim is to extend the capabilities of nanodevices, so as to enable the execution of more complex tasks by means of mutual coordination, achievable through communications. However, although most of these proposals show how devices can communicate at the nanoscales, they leave in the background specific applications of these new technologies. Thus, this paper shows an overview of the actual and potential applications that can rely on a specific class of such communications techniques, commonly referred to as molecular communications. In particular, we focus on health-related applications. This decision is due to the rapidly increasing interests of research communities and companies to minimally invasive, biocompatible, and targeted health-care solutions. Molecular communication techniques have actually the potentials of becoming the main technology for implementing advanced medical solution. Hence, in this paper we provide a taxonomy of potential applications, illustrate them in some detail, along with the existing open challenges for them to be actually deployed, and draw future perspectives