Alfonso Fernandez

Kinematic design of double-wishbone suspension systems using a multiobjective optimisation approach

This paper is focused on the kinematic design of double-wishbone suspension systems in vehicles, which is tackled using a multiobjective dimensional synthesis technique. The synthesis goal is to optimise an RSSR–SS linkage, subject to some constraints involved in the dynamic behaviour of vehicles. The synthesis method is based on gradient determination using exact differentiation to obtain the elements in the Jacobian matrix. These characteristics make the method adapt well to the optimum design of vehicle suspension systems. The method is capable of handling equality and inequality constraints, thus, the usual ranges of values may be imposed on the functional parameters. The formulation presented is easy to implement and the solutions obtained demonstrate the accuracy and robustness of the method.

Comparative study of the effect of PTH (1–84) and strontium ranelate in an experimental model of atrophic nonunion

UNLABELLED This study aimed to set up an experimental model of long bone atrophic nonunion and to explore the potential role of PTH-1-84 (PTH 1-84) and strontium ranelate (SrR). A model of atrophic nonunion was created in Sprague-Dawley rats at the femoral midshaft level. The animals were randomised into four groups. Group A1: control rodents, fracture without bone gap; Group A2: rodents with subtraction osteotomy (non-union model control) treated with saline; Group B: rodents with subtraction osteotomy treated with human-PTH (PTH 1-84); and Group C: rodents with subtraction osteotomy treated with strontium ranelate (SrR). The groups were followed for 12 weeks. X-rays were be obtained at weeks 1, 6 and 12. After sacrificing the animals, we proceeded to the biomechanical study and four point bending tests to evaluate the resistance of the callus and histological study. In second phase, the expression of genes related to osteoblast function was analysed by reverse transcription-quantitative PCR in rats subjected to substraction osteotomy and treated for 2 weeks. The animals were randomised into three groups: Group A2: rodents treated with saline; Group B: rodents treated with PTH 1-84 and Group C: rodents treated with SrR. RESULTS No significant histological differences were found between animals subjected to subtraction osteotomy and treated with either saline or PTH (p=0.628), but significant difference existed between animals receiving saline or SrR (p=0.005). There were no significant differences in X-ray score between the saline and PTH groups at either 6 or 12 weeks (p=0.33 and 0.36, respectively). On the other hand, better X-ray scores were found in the SrR group (p=0.047 and 0.006 in comparison with saline, at 6 and 12 weeks, respectively). In line with this, biomechanical tests revealed improved results in the SrR group. Gene expression analysis revealed a slightly decreased levels of DKK1, a Wnt pathway inhibitor, in rats treated with SrR. CONCLUSIONS SrR increases has a beneficial effect in this atrophic non-union model in rats. This suggests that it might have a role may have important implications for the potential clinical role in the treatment of fracture nonunion.

Optimal Dimensional Synthesis of Linkages Using Exact Jacobian Determination in the SQP Algorithm

This article presents a general method for the dimensional synthesis of mechanisms. This method is based on the well-known Sequential Quadratic-Programming algorithm (SQP). However, several modifications have been introduced in order to improve the robustness and efficiency of the method. One of these modifications in the improved SQP approach is the use of the exact Jacobian instead of the finite differences (FD) methods. The article explains how to obtain the Jacobian for any structural kinematic chain. Furthermore, the method introduces several steps in order to prepare the mechanism for optimization. These steps consist in the translation, rotation, and scaling of the mechanism to be designed. The formulation implemented in the algorithm avoids singular configurations and ensures the assembly of the mechanism providing greater robustness than the conventional approach. In the article, several examples are provided to demonstrate the main characteristics of the method.

Optimal Synthesis Of Mechanisms Generating Open Trajectories Based On Non-linear Position Problems

In this paper a method for more effective structural error quantification in mechanisms generating open trajectories is presented. Generally, mechanism synthesis methods compare the desired curve with the generated curve, taking the mean square distance between the two curves. However, none of these methods is suitable for general application and the problems tackled must fulfil some requirements, for example to be a Grashoff mechanism. Furthermore, to achieve an acceptable final mechanism requires starting the iterations with an initial mechanism that generates a coupler curve similar to the desired one. All these problems are increased due to the difficulty of selecting the most suitable part of the curve when the desired path is an open curve and the curve generated by the mechanism does not coincide in size, orientation and position. The method presented in this paper combines the statistical parameters of both curves with the deterministic ones, in order to compare, without influence ofthe relative orientation, which part of the generated curve best fits the desired one. In this way, the most suitable part of the curve is selected in each iteration, guaranteeing greater speed and efficiency in the final solution with independence fiom the initial mechanism characteristics. The method includes constraint optirnisation in both, the link dimension and the positions of the fixed joints of the mechanism generated.

The Role of MMS and IFToMM Influence in Spain

In this paper a retrospective vision of the development of MMS in Spain is presented. A historical perspective is first outlined and the research carried out in MMS and vehicle engineering is also described. The evolution and changes in education in Spain have been also addressed regarding MMS in the last half century. Not only has the development of new degree plans been analyzed, but also the increase in the number of engineering schools and their impact. Afterwards, future trends in the evolution of MMS in Spain are analyzed. Finally, expectations and critical problems in relation with the field and the scientific community are discussed.

Optimal Design of Steering Mechanisms in Road Vehicles

This paper deals with the design of steering mechanisms in road vehicles. With this aim, the kinematic models of three types of steering linkages are considered and Ackermann steering geometry is used to define the objective function. The proposed method uses a dimensional synthesis technique based on local optimization to obtain the dimensions of the links. The problem is formulated as function generator synthesis, where the inner wheel is supported by the input link and the output link is supported by the outer wheel. The formulation presented in this paper was developed by the authors and it is capable of considering the necessary accuracy conditions in the design of this kind of linkage. Three examples are shown to illustrate the application of the method.Copyright

Supension System Vehicle Design Using a Local Optimization Procedure

This paper deals with the design of double-wishbone and multilink independent suspension systems. To achieve this objective, the proposed method uses a dimensional synthesis technique based on local optimization. An objective function is defined using exact-gradient determination to search for the optimal solution. The multibody system is described by a set of constraint equations which are used to perform the necessary differentiation. Due to the kinematic characteristics of suspension systems, the technique developed here provides a valuable tool for obtaining the optimal solution fulfilling typical requirements imposed in this kind of problems. In this way, double-wishbone and multilink mechanisms are synthesized solving path generation and rigid-body guidance problems at the same time. Finally, two examples are shown to illustrate the application of the method to this kind of systems.Copyright

Path and Function Generation in Planar Mechanism Based on Gradient Determination

The basic idea of the method is to alter the link or links to bring the generated path or function close to the desired one. Planar mechanisms are modelled very easily by means of constraint equations. This approach minimizes the error between the actual path and the desired one when a large number of precision points are required. Large in this context means that only approximate synthesis is possible because the number of equations is much larger than the number of unknowns. The method proposes an objective function as a measurement of the synthesis error. The differentiated expression of the objective function is approximated by means of the Taylor’s series expansion in every increment of the input links. That means that a successive linearization of the differentiated function is used. As consequence, increments considered in the motion must be small enough to avoid errors during the optimization process. Constraints are formulated to obtain the exact gradient elements, avoiding typical problems occurring when approximate methods are used. In this way, a low computational time is necessary because the search direction is always accurate.Copyright

Exact-Gradient Optimization Method for Rigid-Body Guidance Synthesis of Planar Mechanisms

In this paper an approximate kinematic synthesis method is presented with application to rigid-body guidance in planar multibody systems. The problem of finding the optimal dimensions in linkages with rigid-body guidance constraints has been widely studied. Many techniques have been developed and applied to numerous kinematic chains. However, some problems remain without appropriate solution, such as a large number of required poses or low computational cost. The proposed method uses exact-gradient determination to search for an optimal solution. The modelling of the mechanism uses fully Cartesian coordinates and is formulated by means of algebraic constraint equations. Furthermore, the formulation allows the use of a large number of prescribed poses giving high accuracy in the definition of synthesis conditions. Examples are included to illustrate the new approach to some synthesis specifications.© 2004 ASME