Ramon Sancibrian

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.

Effect of cracks and pitting defects on gear meshing

The development of vibration-based condition monitoring techniques, especially those focused on prognosis, requires the development of better computational models that enable the simulation of the vibratory behaviour of mechanical systems. Gear transmission vibrations are governed by the so-called gear mesh frequency and its harmonics, due to the variable stiffness of the meshing process. The fundamental frequency will be modulated by the appearance of defects which modify the meshing features. This study introduces an advanced model to assess the consequences of defects such as cracks and pitting on the meshing stiffness and other related parameters such as load transmission error or load sharing ratio. Meshing forces are computed by imposing the compatibility and complementarity conditions, leading to a non-linear equation system with inequality constraints. The calculation of deformations is subdivided into a global and a local type. The former is approached by a finite element model and the latter via a non-linear Herztian-based formulation. This procedure enables a reduced computational effort, in contrast to conventional finite element models with contact elements. The formulation used to include these defects is described in detail and their consequences are assessed by a quasi-static analysis of a transmission example.

A Model Of Spur Gears Supported ByBall Bearings

In this work a model of a 2D spur gear transmission is described for analysis of tooth contact forces and deformations. Assuming the position of each wheel is known, the contact points between gears are obtained taking into account the geometric description of the tooth profiles including profile errors and relief modifications. Then the deformation in each contact point is separated into a global and a local term combining a finite element model and an analytical formulation originating from Hertzian contact theory. The proposed procedure does not need new element meshing for each angular position thus obtaining an important computational advantage. Afterwards, a non-linear system of equations is obtained and solved for each gear position in order to calculate the meshing contact forces. The model can include the possibility of bidirectional single-flank or double-flank action as well as friction forces in the out-of-action line. Once the contact forces are known, it is possible to use the procedure in the calculation of loaded transmission error and meshing stiffness. Furthermore, each gear is supported by ball bearings that are included in the model taking into account their clearance and their variable stiffness due to the change in the number of balls supporting the load. This variable bearing compliance modifies the gear centre distance and as a consequence the transmission error during a turn. Using this methodology a numerical example is presented where the static behaviour of a spur gear transmission is described and analysed. Special attention is focused on the influence of load level on the final loaded transmission error.

A Dynamic Model For The Study Of GearTransmissions

In this work a previous model developed by the authors for the quasi-static analysis of spur gear transmissions supported by ball bearings was modified extending its capabilities to dynamic analysis. The model combines a finite element and an analytical formulation achieving sufficient accuracy and computational efficiency to make dynamic analysis feasible. Non-linearity associated with the contact among teeth was included, taking into account the flexibility of gears, shafts and bearings. Furthermore, parametric excitations originating both from gear and bearing supports, as well as clearance, were also taken into account. An example of a simple transmission is presented providing several results obtained using the proposed model. Nevertheless, in spite of its usefulness, particularly in the case of variable torque loads, and its improved capabilities compared with other procedures, this approach still requires a high computational effort. As a consequence in those cases where the transmission operates under stationary conditions the formulation could be simplified by using a pre-calculated value for each the gear tooth stiffness as a function of the angular position. Once again, the original model is useful, taking advantage of its computational efficiency in the calculation of these stiffness coefficients throughout a meshing period. The improved model is applied to the same transmission and the consequences of a misleading calculation of the stiffness coefficients are shown. Then, it was used to study the vibratory behaviour under different levels of applied torque, showing the modifications suffered by the orbits, meshing contact forces and particularly the spectra obtained for bearing forces.

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.

A study of the prevalence of musculoskeletal disorders in surgeons performing minimally invasive surgery

Introduction. Minimally invasive surgery (MIS) has shown significant benefits for patients and healthcare systems. However, due to the poor ergonomic adaptation of operating rooms and surgical instruments, most surgeons suffer from pain caused by musculoskeletal disorders (MSDs). Methods. A descriptive survey on MIS surgeons working in different surgical specialties has been carried out in Hospital Valdecilla (Spain). The aim is to determine the prevalence of MSDs using a personal interview and the standardized Nordic questionnaire. The study determines the prevalence of MSDs in different parts of the body and their relationship with epidemiological and labor variables. A questionnaire was filled out by 129 surgeons. Results. 90% of surgeons reported MSDs. The higher prevalence appears in the most experienced surgeons. The most affected zones are the lower back (54%), neck (51%), upper back (44%), lower extremities (42%), right shoulder (29%) and right hand (28%). Conclusions. The prevalence of MSDs is higher in MIS surgeons than in any other occupational group. The most vulnerable group is experienced surgeons and there is a potential risk that symptoms will be increased in the future. Muscle strength is revealed as a protective factor against MSDs.

MANAGEMENT AND ASSESSMENT OF HERITAGE BUILDINGS IN THE CITY OF HAVANA THROUGH THE PRIORITIZATION OF EMERGENCY ACTIONS

Declared a World Heritage Site by UNESCO, in 1982, the Historical Center of Havana, occupying an area of 2.14 km, has 3,510 buildings, many of which now severely dilapidated. In fact, the Historical Center is in need of preferential action, due to the severity of the deterioration of its buildings. The situation is continually worsened following each hurricane season, and their accompanying tropical storms that have caused irreparable damage to buildings over the years. After a careful inspection of the heritage buildings of the Historical Center, it was possible to identify those in danger of imminent collapse and those with a useful life that could be prolonged through the implementation of the necessary emergency actions. In response to both challenges, a multi-criterion instrument based on the MIVES system was applied, with the purpose of prioritizing in an objective and justifiable way the necessary repairs and degrees of intervention. This instrument is based on requirements, criteria and indicators, all of which are selected, analysed and approved by a specially appointed panel of experts that quantifies all the factors in the value chain.

A METHOD FOR ASSESSING CREATIVITY AND INNOVATION OF INDUSTRIAL PRODUCTS BY ENGINEERING STUDENTS

In this paper experiences about the implementation of creative activities in industrial engineering degrees are related. These activities were used in engineering courses to improve the creative skills of the students. Thus, the main goal was to make them capable to design innovative products using ideation methods and working in groups. Although there are some works in the literature about the implementation of creative methods in engineering degrees none of them have established well defined approaches which are able to assess the creativity and innovation level of products in an effective way. Indeed, one of the main problems that have been found by instructors during the classes is how students can evaluate their own creative solutions and the degree of innovation of the designed products. There are no many works in the literature focusing in this topic and all of them have been developed to be applied by engineers with long experience in design. These methods measure the innovation of products by the quantification of a number of factors. However, these factors present some difficulties for students who are not used to work with them. In fact, one of the main problems found by instructors in implementing creativity procedures at university level is that students do not have enough experience about the assessment of engineering products and their degree of innovation. This paper describes a new procedure for the measurement of the level of creativity that new ideas provide. It can be also used for the measurement of the innovation of products. A case study is presented to illustrate the method and evaluate its effectiveness. In this activity an engineering design problem is proposed to the students and they have to find the best solution. Brainstorming is used as idea generation method and they have to measure their creativity using the proposed approach. The main advantage of the method is that it can be easily used by students and instructors. In this way the students can evaluate their own ideas in order to sort them and select the most creative ones. The method works with a three dimensional scale which are level, scope and goals. The comparison of the proposed method with other existing approaches allows highlighting the easier understanding of the factors to be evaluated.

Thermal Imaging-Based Muscular Activity in the Biomechanical Study of Surgeons

The use of minimally invasive surgery has introduced many modifications in surgical procedures. Despite the advantages that this kind of surgery provides, surgeons have to confront many ergonomic problems during their interventions. In fact, the poor ergonomic characteristics of the workplace reduce the efficiency of the interventions and produce undesirable effects such as physical fatigue or musculoskeletal injuries. Electromyography has been used traditionally for measurement of the muscular effort in the workplace. However, in recent studies thermal imaging has been highlighted as a valuable alternative in the determination of muscular activity. One of the main advantages of using thermal imaging is that there is no necessary to foresee the muscular groups activated in the performance of surgery. In this paper thermal imaging is used to evaluate the muscular effort of surgeons and the results are compared with electromyography. The paper shows the features of this technique and the relationship with electromyography.