E. Amezua

Judder vibration in disc brakes excited by thermoelastic instability

Friction vibrations and noises which are common in brakes, have attracted a great deal of attention lately. This paper analyses low frequency vibrations in disc brakes excited at high car speed. This vibration, called judder, has a frequency in the range 10 to 300 Hz and usually comes in association with hum noises. The dynamic phenomenon shows two principal components, one normal and the other one tangential to the disc brake surface. It is explained how variations of friction coefficient, and thermoelastic instability caused by the tangential component, contribute to the appearance of judder. A numerical analysis in 3D using the finite element method has been implemented combining both tangential and normal components, and solving the thermoelastic process. Special attention is dedicated to the simulation of the thermoelastic process showing the correlation with experiments.

A Parallelogram-Based Parallel Manipulator for Schonflies Motion

A parallelogram-based 4 degrees-of-freedom parallel manipulator is presented in this paper. The manipulator can generate the so-called Schonflies motion that allows the end effector to translate in all directions and rotate around an axis parallel to a fixed direction. The theory of group of displacements is applied in the synthesis of this manipulator, which employs parallelograms in every limb. The planar parallelogram kinematic chain provides a high rotational capability and an improved stiffness to the manipulator. This paper shows the kinematic analysis of the manipulator, including the closed-form resolution of the forward and inverse position problems, the velocity, and the singularity analysis. Finally, a prototype of the manipulator, adding some considerations about its singularity-free design, and some technical applications in which the manipulator can be used are presented.

A finite element approach to the position problems in open-loop variable geometry trusses

The present paper looks at some kinematic and static-equilibrium problems that arise with variable-geometry trusses (VGTs). The first part of the paper looks at the use of active controls in the correction of static deformations, the second part at the position problems. The separation between deformable- and rigid-body displacements makes it possible to consider separately the corrections in each component of the structure. VGTs are considered as open-loop linkages with redundant rigid-body degrees of freedom. Owing to this redundancy, possible solutions to the inverse problem are in general infinite, for which reason it is necessary to use some optimization criteria. To tackle the problem an optimization procedure with constraints is developed for the purpose of minimizing the displacements of the actuators. Suitable use of the constraints allows us to solve the direct position problem using the same optimization procedure.

Multiple points on the coupler curve of transitional four-hinge planar linkages

Abstract In the present paper a detailed analysis is made of the conditions governing the existence and position of multiple points on the coupler curves of a four-hinge linkage. It is shown that apart from the circle of singular foci there exists another “complementary curve” on which also there may be multiple points. An analysis is made of the case of transitional mechanisms, in which there are double points outside the circle of singular foci but lying on the complementary curve. A detailed look is then taken at the conditions for the position of threefold points and cusps, which must be both on the circle of singular foci and on the complementary curve. In addition there is a description of two simple procedures for the graphic synthesis of transitional mechanisms with threefold points on their coupler curve.

An adaptive procedure for the finite element computation of non‐linear structural problems

The present paper proposes a procedure for the resolution of non‐linear structural problems. It includes a study of the reliability of the results and the adaptive meshing. The iterative phase of the solution of the equilibrium equations entails an adaptive strategy for updating the tangent stiffness matrix, with a control of the load step. This results in a higher rate of convergence for the iterative process. The mechanical deformation processes here considered may give rise to considerable geometric distortion in the finite elements of the mesh. If they do, the consequence will be not only that the FE analysis fails to yield precise results, but also, owing to problems deriving from the numerical ill‐conditioning, that continuation may be impractical. To facilitate the study of these results, we developed an error estimator of the flux projection type, which is based on the mechanical deformation power. It is also used as a refinement criterion for the FE mesh. Distorted meshes can be fully or partiall...

Software Tool to Compute, Analyze and Visualize Workspaces of Parallel Kinematics Robots

The aim of this paper is to present a new software tool designed to compute and allow visualization of the different types of workspaces of parallel manipulators in the most user-friendly and efficient way. The graphical interface of this program makes it possible to define the geometrical scheme of the robot. All required parameters of the kinematic model can be set easily and quickly. Given that the workspace of a parallel manipulator is a complex entity, this CAD tool has implemented all the controls needed to visually define all the complicated parameters required to launch a workspace computation. Once the calculations are performed, the challenging task of visualizing the results has been optimized. Due to the circumstance that a workspace can be a higher than three-dimensional (3-D) mathematical entity, which cannot be graphically represented, the user can choose the specific variables (two or three) onto which to project the workspace obtained (2-D or 3-D representations). Within these surfaces and volumes, several color maps, associated with kinematic indicators, can be traced to enable the most efficient path planning of the manipulator analyzed.

Analysis of the components of discretization error in non-linear structural problems

The present paper considers the reliability of finite-element analysis where non-linear planar structural problems (large strains and plasticity) are concerned. Error estimators of the flux-projection type, based on strain power density, are used. A study of the various components of error discretization is made as a function of parameters such as load step or the number of degrees of freedom of the finite-element model. Two numerical examples are selected so that certain properties of these estimators are demonstrated. Conclusions of practical use can be drawn from the results expressed in tables and charts.

Modal Characterization of the Instantaneous Mobility of Manipulators

In this paper, a computational approach suitable to compute the instantaneous mobility of manipulators in any kind of configuration (either singular or nonsingular) using a general purpose software is presented. Although the procedure is applicable to any formulation of the velocity equation, in this paper authors have used a point-based jacobian formulation of the manipulator. The end-effector’s instantaneous mobility is analyzed, first discriminating among its rotational, translational and passive freedoms, and then computing its principal screws. Then, either its instantaneous screw systems or certain instantaneous pitch surfaces can be depicted. The approach is illustrated with its application to the 3-URU DYMO parallel manipulator.Copyright

A Robot for Welding Inspection in Offshore Mooring Chains

In this paper, the authors present the CIRUS robot. This automatic system uses a combination of pulse-echo and pitch and catch ultrasonic strategies for the inspection of the welded area of mooring chain links in an automatic way. The robot is divided in three parts: global positioning subsystem, local positioning subsystem and inspection subsystem. Additionally, a data acquisition subsystem processes the results of the verification and produces a report for the inspector allowing the traceability of the product for assuring the welding quality.

A robot for non-destructive testing weld inspection of offshore mooring chains

Welding flaw detection is a key step in manufacturing many components. In offshore chains, every link is manufactured from a steel bar that is bent and the ends joined by flash butt welding. Ultrasonic inspection of the welded area is required for classification. Defects, if any, are parallel to the welded area, which do not favour detection by manual inspection with 45° beams, as per usual practice . This article reports on CIRUS, a robot developed for automatic inspection of the weld area using a combination of pulse-echo and pitch-catch ultrasonic testing. The robot kinematic structure includes global positioning, local positioning and inspection subsystems, and each subsystem design is described in detail. A data acquisition system processes ultrasonic inspection results and provides visual information for the inspector as well as traceability for quality manufacturing.