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Carbonate hydroxyapatite (CHAp) was synthesized from domestic hen eggshells by using three alternative wet chemical methods at room temperature. In the first method, the powdered eggshells were reacted directly with H3PO4. In the other two methods, calcium acetate was obtained in a first step by dissolving the eggshells in acetic acid. Then, calcium acetate was reacted with Na3PO4•12H2O and (NH4)2HPO4 in the second and third methods, respectively. The synthesized CHAp was characterized by X-Ray Diffraction (XRD), Fourier Transformed Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Fine and poorly crystallized CHAp was obtained under all experimental conditions employed. Among all synthesized materials, the one produced by the first method showed the closest resemblance to bovine bone, which was related to similar carbonate contents in both materials. In general, acicular CHAp crystals with a size ranging from 10 to 100 nm were obtained, which had an aspect ratio of ∼1/4. The morphology of the synthesized CHAp crystals was consistent with their estimated carbonate content.Se sintetizó carbonato-hidroxiapatita (CHAp) a partir de cascarón de huevo de gallina, usando tres métodos químicos alternativos vía húmeda a temperatura ambiente. En el primer método, el cascarón pulverizado fue hecho reaccionar directamente con H3PO4. En los otros dos métodos, el primer paso fue la obtención de acetato de calcio mediante la disolución del cascarón en ácido acético. Luego, el acetato de calcio fue hecho reaccionar con Na3PO4•12H2O y (NH4)2HPO4 en el segundo y tercer método, respectivamente. El CHAp sintetizado fue caracterizado por difracción de rayos X (DRX), espectroscopia infrarroja por transformada de Fourier (FT-IR), microscopía electrónica de barrido (MEB) y microscopía electrónica de transmisión (MET). Bajo todas las condiciones experimentales empleadas se obtuvo CHAp fina y poco cristalina. De entre todos los materiales sintetizados, el producido empleando el primer método mostró la mayor similitud con respecto al hueso de bovino, lo cual fue relacionado con un contenido similar de carbonato en ambos materiales. En general, se obtuvieron cristales aciculares de CHAp con un tamaño en el rango de 10 a 100 nm, los cuales presentaron una relación de aspecto de ∼1/4. La morfología de los cristales de CHAp sintetizados fue consistente con su contenido estimado de carbonato.

In the present work, we studied a “Mixed Alkaline–Earth Effect”, i.e. the non-linear behaviour showed by the glass transition temperature as well as by the compressive strength of glasses of the CaO-MgO-Al2O3-SiO2 system, when a part of the CaO contained in them was substituted by a BaO/SrO mixture, in variable molar proportions. An important factor for the occurrence of this phenomenon was the difference in atomic weight, ionic radii and field strength of the Ba2+ and Sr2+ ions in comparison with those corresponding to the Ca2+ ion. Another factor considered was the likely occurrence of a microphase separation caused by the addition of BaO and/or SrO, together with the presence of F- and Mg2+ in the glasses. Other glass properties studied as a function of the CaO substitution level were density, glass molar volume, oxygen molar volume, packing fraction, and chemical resistance in neutral, basic and acidic aqueous media. In general, the structural reinforcement of the glass network caused by the partial substitution of CaO by a BaO/SrO mixture was accompanied by an improvement in the alkaline resistance of the materials, which were found to be suitable for applications in corrosive environments, especially in basic media. Keywords: Mixed alkaline–earth effect; CaO-MgO-Al2O3-SiO2 system; glass properties.En el presente trabajo, se estudia el comportamiento no lineal mostrado por la temperatura de transición vítrea y por la resistencia a la compresión de vidrios del sistema CaO-MgO-Al2O3-SiO2, cuando una parte del CaO contenido en los mismos es sustituido por una mezcla de BaO/SrO, en relación molar variable. Factores importantes para que se de este comportamiento son la diferencia entre pesos atómicos, radios iónicos e intensidad de campo de los iones Ba2+ y Sr2+ y los del propio ión Ca2+. Otro factor considerado ha sido la probable existencia de una separación de microfases originada por la adición de BaO y/o SrO, junto con la presencia de flúor y magnesio en los vidrios. Otras propiedades estudiadas, en función del CaO sustituido, han sido la densidad, el volumen molar del vidrio, el volumen molar del oxígeno, la fracción de empaquetamiento, y la resistencia química en medios acuosos neutros, básicos y ácidos. En general, el refuerzo estructural del retículo vítreo causado por la sustitución parcial del CaO por una mezcla de BaO/SrO viene acompañada por una mejora en la resistencia alcalina, lo que hace que estos materiales sean adecuados para aplicaciones en ambientes corrosivos y especialmente en medios básicos.

Lanthanum chromite nano-particles, with a composition of La0.9Ca0.1CrO3 and La0.8Ca0.2CrO3, were produced by 1 h of hydrothermal reaction at 400 and 425°C respectively. The sintering of the powders was conducted using a spark plasma apparatus over the temperature range 1300-1550ºC for 1 min with a constant loading pressure of 45 MPa. Additional sintering experiments using conventional firing were carried out for comparison. Fully densified (98 % r.d.) lanthanum chromite pellets with fine equiaxial grains 2.3 μm in size were obtained using the SPS (spark plasma sintering) method. In contrast, a maximum relative density of 97 % was produced using La0.8Ca0.2CrO3 sintered conventionally at 1400ºC for 300 min, and the average grain size of the resulting sintered sample was 6 μm.Partículas ultrafinas de cromita de lantano, con una composición de La0.9Ca0.1CrO3 y La0.8Ca0.2CrO3, se obtuvieron después de 1 hora de síntesis hidrotermal a las temperaturas de 400 y 425°C respectivamente. Los compuestos obtenidos, con un tamaño de partícula de ~ 200 nm, se caracterizaron utilizando las técnicas de DRX, MEB y MET. La sinterización de estos polvos se efectuó en un equipo de chispa de plasma en el rango de temperatura de 1300-1500°C durante 1 min, y a una presión de compactación de 45 MPa. Ambos polvos también se sinterizaron siguiendo un tratamiento térmico convencional, en aire, con el propósito de comparar ambos métodos de sinterización. Las muestras de cromita de lantano sinterizadas por plasma presentaban una densidad relativa del 98 % (/t); y una microestructura monofásica con granos equaxiales con un tamaño medio de grano menor de 2.3 μm. En contraste, la composición La0.8Ca0.2CrO3, sinterizada a 1400°C/300 min, por métodos convencionales alcanzó una densidad relativa máxima del 97 % y su microestructura estaba formada por una sola fase con un tamaño medio de grano de 6 μm.

The present work has been conducted aiming to develop additional phase [Ca3SiO5, Ca2SiO4 and/or Ca3Mg(SiO4)2]-bonded magnesia refractory materials via reaction sintering of dolomite-zircon mixtures, employing a Mexican dolomite containing an excess of 3 wt% of CaCO3. The study was based on phase equilibrium data extracted from the quaternary system CaO – MgO – SiO2 – ZrO2, to put it more precisely, base on the projection from the MgO-apex of the liquidus surface of the primary crystallization volume of MgO onto the opposite face of the above mentioned quaternary system. The refractory materials designed within this system were obtained by attrition milling, followed by cold isostatic pressing and high temperature reaction sintering. All initial and produced materials were characterized by ICP-AES, XRF, XRD, SEM-EDX, DTA and TG analyses. The results obtained indicated that reaction sintering of dolomite-zircon mixtures is an interesting route to produce MgO-CaZrO3-additional phase refractory materials.El propósito de este trabajo ha sido obtener materiales refractarios de magnesia, aglomerados con una fase adicional [Ca3SiO5, Ca2SiO4 y/o Ca3Mg(SiO4)2], mediante la sinterización reactiva de mezclas de dolomita-circón, empleando para ello una dolomita mexicana que contiene un exceso de 3% en peso de CaCO3. El estudio se basa en la información relativa al equilibrio de fases del sistema CaO – MgO – SiO2 – ZrO2. En concreto se usa la proyección, desde el vértice del MgO, de la superficie de liquidus del volumen de cristalización primaria de este, hacia la cara opuesta de sistema cuaternario. Los materiales refractarios diseñados se han obtenido por molienda de atrición, seguida de un prensado isostático en frío y sinterización reactiva a alta temperatura. Todos los materiales, iniciales y finales, han sido caracterizados mediante ICPAES, FRX, DRX, MEB-EDX, ATD y TG. Los resultados obtenidos indican que la sinterización reactiva de las mezclas de dolomita-circón es una ruta interesante para la producción de materiales refractarios de MgO-CaZrO3-fase adicional.

The multiobjective optimization of a four-degree-of-freedom symmetric parallel manipulator for Schonflies-motion generation is the subject of this paper. First, the inverse positioning problem is discussed, along with its velocity analysis. The workspace is then analyzed, thereby deriving a closed-form expression of the workspace volume, which depends on the orientation of the moving platform. Next, the isotropic design of the manipulator is obtained. Then, the dexterity analysis of the manipulator is conducted, which is one objective of the optimum design of the manipulator, a second objective being a normalized workspace volume. Finally, the results of the optimization process are reported in terms of a set of Pareto-optimum pairs of the design parameters. [DOI: 10.1115/1.3066659] Keywords: parallel manipulator, Schonflies-motion, optimization, multiobjective

The design of a novel prismatic drive is reported in this paper. This transmission is based on Slide-o-Cam, a cam mechanism with multiple rollers mounted on a common translating follower. The design of Slide-o-Cam was reported elsewhere. This drive thus provides pure-rolling motion, thereby reducing the friction of rack-and-pinions and linear drives. Such properties can be used to design new transmissions for parallel-kinematics machines. In this paper, this transmission is intended to replace the ball-screws in Orthoglide, a three-dof parallel robot intended for machining applications. [DOI: 10.1115/1.2198283]

Although bevel-gear robotic wrists are widely used in industrial manipulators due to their simple kinematics and low manufacturing cost, their gear trains function under rolling and sliding, the latter bringing about noise and vibration. Sliding is inherent to the straight teeth of the bevel gears of these trains. Moreover, unavoidable backlash introduces unmodeled dynamics, which mars robot performance. To alleviate these drawbacks, a gearless pitch-roll wrist is currently under development for low backlash and high stiffness. The wrist consists of spherical cam-rollers and spherical Stephenson linkages, besicles two roller-carrying disks that drive a combination of cams and Stephenson mechanisms, the whole system rotating as a differential mechanism. The paper focuses on the design of the chain of spherical Stephenson mechanisms. The problem of the dimensional synthesis is addressed, and interference avoidance is discussed. An embodiment of the concept is also included. Keywords: spherical Stephenson mechanism, dimensional synthesis, nonlinear least-square optimization, pitch-roll wrists

Methods of structural optimization have been studied and developed over the last three decades. An important aspect of structural optimization pertains to the condition under which the loads are applied. Most machine structures in operation are subject to loads varying as functions of time. In this paper, a novel approach is proposed to cope with loads whose magnitudes vary within given bounds and with variable directions. The underlying ideas are applied to the structural optimization of the roller-carrying disk of a novel class of cam-follower speed reduction devices termed Speed-o-Cam (SoC). Results obtained in this paper are compared with a current prototype and with an intermediate design in which the dimensions of the roller pins are optimized. Combined with the optimum dimension of the roller pins, our structural-optimization results lead to an improvement of almost twice the stiffness with a mass reduction of 40% of the original prototype. [DOI: 10.1115/1.1825442]

The vibration of linear mechanical systems with arbitrary damping is known to pose challenging problems to the analyst, for these systems cannot be analyzed with the techniques pertaining to their undamped counterparts. It is also known that a class of damped systems, called proportionally damped, can be analyzed with the same techniques, which mimic faithfully those of single-degree-of-freedom systems. For this reason, in many instances the system at hand is assumed to be proportionally damped. Nevertheless, this assumption is difficult to justify on physical grounds in many practical applications. What this assumption brings about is a damping matrix that admits a simultaneous diagonalization with the stiffness matrix. Proposed in this paper is a decomposition of the damping matrix of an arbitrarily damped system allowing the extraction of the proportionally damped component, which, moreover, approximates optimally the original damping matrix in the least-square sense. Finally, we show with examples that conclusions drawn from the proportionally damped approximation of an arbitrarily damped system can be dangerously misleading. [DOI: 10.1115/1.1483832]

This paper introduces a new approach to sequential quadratic programming. Upon application of the orthogonal-decomposition algorithm and the Gerschgorin Theorem for the stabilization of the Hessian matrix in the quadratic-programming solution, this novel approach offers an alternative to existing methods that, additionally, dispenses with a feasible initial guess.

The design of a novel transmission for speed reduction is reported in this paper. The transmission is based on the layout of pure-rolling indexing cam mechanisms, for it is intended to eliminate backlash and friction, which are the main drawbacks of gear transmissions. The design relies on a unified methodology for indexing cam mechanisms, whereby the same procedure is used to design planar, spherical, and spatial mechanisms. Two versions of the speed reducer, that we term Speed-o-Cam, are described here, namely, planar, to couple shafts of parallel axes, and spherical to couple shafts of intersecting axes. By means of a cascade of two planar versions of Speed-o-Cam, moreover, coaxial shafts can be coupled. Moreover, contrary to other alternatives to gear transmissions, such as harmonic drives or epicyclic transmissions, Speed-o-Cam caters to shafts with either parallel or intersecting axes; in the latter case, moreover, the angle at which the axes intersect can vary from 0 degrees to 180 degrees continuously. The design with shaft axes at 0 degrees leads to an internal cam, i.e., one with its axis external to the axes of the follower and the roller in contact; for shaft axes at 180 degrees, the design leads to an external cam, i.e., one with its axis lying between those of the follower and the roller in contact.

Two versions of spatial double-triangular mechanisms are introduced, one with three and one with six degrees of freedom. Using dual-number quaternion algebra, a formula for the direct kinematics of these manipulators is derived. Numerical examples are included.

In this paper, we introduce a new class of parallel manipulators, called general hybrid parallel manipulators (GHPM). These are modular manipulators that may contain serial subchains as well as subchains of parallel modules, acting in parallel and connecting a base to a common platform. The instantaneous motion of the GHPM is studied by resorting to the theory of screws. In this context, we define the screw-system annihilator to reduce, systematically, the number of unknowns involved to a minimum. The formulation presented here is general and can be applied to most existing parallel manipulators, multifingered hands, multiple coordinated robots and walking machines. To illustrate the basic symbolical and numerical aspects of the proposed procedure, the analyses of the instantaneous kinematics of two hybrid manipulators are included.

A general scheme for the optimization of planar, spherical and spatial bimodal linkages for function generation is proposed. The problem is solved here following two basic steps: (i) planning input-output ((I/0) curves based on design requirements and selecting data from the planned curve; and (ii) setting up an optimization procedure to minimize a performance index.

In this paper the ruled surfaces of two rigid bodies that are in contact while moving with a prescribed time-varying angular-velocity ratio are generated. These are then used as the contact surfaces of indexing cam mechanisms. In this way, planar, spherical, and spatial mechanisms are synthesized in a unified framework, the pressure angle, for all these cases, being analyzed. The approach is illustrated with various examples.

The solid modeling of bevel gears has been recognized as a major design challenge. Various approaches have been proposed to approximate the theoretical involute-generated contact surface of bevel gears. As a means to accurately represent contact surfaces of these gears, the exact spherical involute is introduced here. The solid models of straight and spiral bevel gears are obtained by applying simple sweeping techniques to their tooth profiles, which are described by the exact spherical involute. Furthermore, the volumetric properties of the modeled bevel gears are readily computed from their piecewise-linear approximation.

This paper follows an accompanying one on the constrained minimization of cam profiles with translating flat-face followers. Here, the corresponding problem for oscillating flat-face followers is discussed. The unconstrained optimization of this type of cam mechanisms, aimed at the minimization of the area of the cam disk, has been reported elsewhere. In this paper we recognize that unconstrained cam-size minimization can lead to profiles with curvature discontinuities, i.e., cusps, which should be eliminated, for they give rise to inadmissibly large contact stresses. The conditions under which curvature discontinuities arise are derived. These conditions lead to a simple constrained minimization procedure, whose application is illustrated with a fully solved numerical example.

A novel method of synthesis of the surface geometry of spherical cam-oscillating roller-follower mechanisms is introduced. The approach aims at zeroing the sliding velocity between the cam and the roller, their respective geometries being thus obtained as conical surfaces. The pressure angle is analyzed in detail. Specific results are presented for the application of this synthesis technique to indexing cam mechanisms.