Jorge Santolaria Mazo

Design and Mechanical Evaluation of a Capacitive Sensor-Based Indexed Platform for Verification of Portable Coordinate Measuring Instruments

During the last years, the use of Portable Coordinate Measuring Machines (PCMMs) in industry has increased considerably, mostly due to their flexibility for accomplishing in-line measuring tasks as well as their reduced costs and operational advantages as compared to traditional coordinate measuring machines (CMMs). However, their operation has a significant drawback derived from the techniques applied in the verification and optimization procedures of their kinematic parameters. These techniques are based on the capture of data with the measuring instrument from a calibrated gauge object, fixed successively in various positions so that most of the instrument measuring volume is covered, which results in time-consuming, tedious and expensive verification procedures. In this work the mechanical design of an indexed metrology platform (IMP) is presented. The aim of the IMP is to increase the final accuracy and to radically simplify the calibration, identification and verification of geometrical parameter procedures of PCMMs. The IMP allows us to fix the calibrated gauge object and move the measuring instrument in such a way that it is possible to cover most of the instrument working volume, reducing the time and operator fatigue to carry out these types of procedures.

Development of a New Calibration Procedure and Its Experimental Validation Applied to a Human Motion Capture System

Motion capture systems are often used for checking and analyzing human motion in biomechanical applications. It is important, in this context, that the systems provide the best possible accuracy. Among existing capture systems, optical systems are those with the highest accuracy. In this paper, the development of a new calibration procedure for optical human motion capture systems is presented. The performance and effectiveness of that new calibration procedure are also checked by experimental validation. The new calibration procedure consists of two stages. In the first stage, initial estimators of intrinsic and extrinsic parameters are sought. The camera calibration method used in this stage is the one proposed by Tsai. These parameters are determined from the camera characteristics, the spatial position of the camera, and the center of the capture volume. In the second stage, a simultaneous nonlinear optimization of all parameters is performed to identify the optimal values, which minimize the objective function. The objective function, in this case, minimizes two errors. The first error is the distance error between two markers placed in a wand. The second error is the error of position and orientation of the retroreflective markers of a static calibration object. The real co-ordinates of the two objects are calibrated in a co-ordinate measuring machine (CMM). The OrthoBio system is used to validate the new calibration procedure. Results are 90% lower than those from the previous calibration software and broadly comparable with results from a similarly configured Vicon system.Motion capture systems are often used for checking and analyzing human motion in biomechanical applications. It is important, in this context, that the systems provide the best possible accuracy. Among existing capture systems, optical systems are those with the highest accuracy. In this paper, the development of a new calibration procedure for optical human motion capture systems is presented. The performance and effectiveness of that new calibration procedure are also checked by experimental validation. The new calibration procedure consists of two stages. In the first stage, initial estimators of intrinsic and extrinsic parameters are sought. The camera calibration method used in this stage is the one proposed by Tsai. These parameters are determined from the camera characteristics, the spatial position of the camera, and the center of the capture volume. In the second stage, a simultaneous nonlinear optimization of all parameters is performed to identify the optimal values, which minimize the objective function. The objective function, in this case, minimizes two errors. The first error is the distance error between two markers placed in a wand. The second error is the error of position and orientation of the retroreflective markers of a static calibration object. The real co-ordinates of the two objects are calibrated in a co-ordinate measuring machine (CMM). The OrthoBio system is used to validate the new calibration procedure. Results are 90% lower than those from the previous calibration software and broadly comparable with results from a similarly configured Vicon system.

Mechanical design of an indexed metrology platform for verification of portable coordinate measuring machines

The demand of faster and reliable measuring tasks for the control and quality assurance of modern production systems creates new challenges for the field of coordinate metrology. Thus, search for new solutions in coordinate metrology systems and development of existing ones that respond to industry’s demands still persists. An example of such coordinate metrology systems are the portable coordinate measuring machines (PCMMs), which use in industry has considerably increased during the last years, mostly due to their flexibility for accomplishing in-line measuring tasks as well as their reduced costs and operational advantage as compared to traditional coordinate measuring machines (CMMs). In this work, the mechanical design of an indexed metrology platform (IMP) is presented. The aim of the IMP is to increase the final accuracy and radical simplification of the calibration, identification and verification of geometrical parameters procedures of PCMMs.

Comparison of Double Flank Roll Testers for Worm and Worm Gear

Roll testing is the most direct way and simple method of checking the functional accuracy of the gear by means of the geometric and rolling parameters obtained in the test. Nevertheless, for the time being there is no standard calibration procedure which could be applied to this type of rolling testers. In spite of trying to reproduce the tests in the three double flank roll testers under the same testing conditions and procedure, big variations in the results obtained were detected. This demonstrates the need to create a norm which could give a unique trazability procedure for this kind of tests and their testers calibration.

Double Flank Roll Testing as Verification Technique for Micro Gears

In recent years there has been a considerable interest in microsystems, named as MEMS (Micro Electromechanical Systems). Its continuing expansion is expected, derived from the trend towards miniaturization of components and the increasing applications for these micro devices. To overcome this, the technology to produce these products known as microsystem technology (MST), has been improving in order to allow the manufacturing of this type of parts becoming of growing importance over the past years. Micro gears are commonly used in electronics industry where the miniaturization process follows a constant evolution with multiple use advantages despite their small size. In this work the study and analysis of the existing verification techniques for micro gears together with the definition of a double flank rolling test focused on these gears is presented.

PROGRAMACIÓN DE UNA CÉLULA ROBOTIZADA PARA SOLDADURA DE COMPLEMENTOS A DEPÓSITOS DE ACERO A PRESIÓN

Welded steel tanks are pressure containers whose function is to store a pressure fluid. Nowadays, industrial robots develop a very important work in the industry, and especially in welding systems. The automation of welding processes has many advantages. However, reprogramming of the control system to change production models remains difficult and requires a lot of time. The objective of this work is to develop a methodology to reprogram the control system of a robot welding in a simple and quick way for a considerable time saving. To do this, from the definition of the layout of the welding cell , a method to systematize the process of obtaining the programs has been developed so that the robot cell perform the welding process of the elements connected to the ferrule of the tank. The method consists in the definition of a structured data with a geometric description of the tank and the parameters of the welding process. The method adds the calculated data to a file using several computer programs that allow the robot cell perform welding paths. These data are the points and orientations of the end effector and robot coordinates joint obtained by the Denavit - Hartenberg method. The generated data file is then loaded into the simulation environment of the robot to verify the paths and make corrections. Once validated the simulation program, the robot program is generated and automated welding is performed. The programs have been generated in a parameterized way, so changing them is simple and quick.

Análisis y mejoras en el diseño de un mecanismo cinemático de alta precisión

A new design for reducing the kinematic mechanism error is presented in this paper. Firstly, a prototype having a universal joint is presented and the kinematic model in the Simmechanics environment of Matlab is described, studying the system behaviour by means of simulation. Then, the manufacturing and assembly of the platform is performed and the mechanism performance is evaluated. To do this, different tests are carried out in which the mechanism backlash and the influence of the elevation angle and the misalignment in every axis due to backlash are analyzed. Finally, the mechanism design is improved by replacing the universal joint with a new element that consists on bearings and precision locknuts. This element allows us to obtain the two desired degrees of freedom. The replacement of the commercial universal joint by the developed element implies a considerably increment of the mechanism accuracy. The developed platform has many applications in the industry, such as, machining tool processes, high range metrology, holder base for measurement tools such as topography instruments, mirror orientation in telescopes, etc.

ESTUDIO DEL ÁNGULO DE GIRO DE ELEMENTOS FLEXIBLES APLICADO A MECANISMOS PARALELOS

ABSTRACT This paper analyses the flexible hinge parasitic error in function of the rotation angle in the 0-45o range. First, an analysis of the different geometries -taking into account considerations such as the stiffness and the rotation angle- is carried out, and a new kinematic model of two degrees of freedom parallel mechanism is developed. This mechanism consists of a exible system that allows us to obtain the azimuth and elevation angles. The model developed is based on the Denavit-Hartenberg method. The kinematic chain containing flexible elements is therefore modelled by adding ransformation matrices that consider the angle and translation error of those elements with respect to the initial reference systems. Subsequently, he flexible hinge geometric parameters are determined, by means of a simulation software based on the finite element method in order to obtain a system that allows us to perform the desired rotations. Finally, the element has been experimentally characterized, for two selected materials: aluminium EN AW-7075 and steel F-1430 and the rotation axis error in function of the rotated angle is obtained. This characterization let us observe which material is more suitable in function of the work range, and know for a particular application, the rotation magnitude that can be achieved with the flexible element in function of the desired accuracy.

ANALISIS DEL JUEGO, REPETIBILIDAD DEL POSICIONAMENTO Y PRECARGA DE UN MECANISMO PARALELO.

complejidad existente en el desarrollo de los modelos matematicos de los mecanismos paralelos, es necesario realizar un analisis previo de los errores caracteristicos del sistema. En este trabajo se determina el juego y la repetibilidad de posicionamiento de un mecanismo paralelo de dos grados de libertad giratorios, y se analiza la precarga necesaria para aumentar la precision del sistema. Inicialmente se revisa la bibliografia especializada en el diseno y caracterizacion de mecanismos basados en cinematica paralela. En la mayoria de los estudios analizados, los errores como el juego son absorbidos por el modelo matematico sin caracterizar los componentes ni analizar cuales de los errores del sistema son los mas determinantes. Posteriormente se presenta la metodologia utilizada para la caracterizacion de los componentes del sistema de posicionamiento. Para ello, se describen los procedimientos y los utillajes utilizados para cada equipo de medida y se comparan los diferentes sistemas de medicion utilizados como sensores opticos lineales, interferometro laser y palpadores inductivos. Los resultados obtenidos muestran errores de juego del actuador en tomo a los 45 11m con una desviacion del error de 311m. La aplicacion de una precarga a contraccion sobre la rotula esferica permite obtener un juego menor de 3 i.1m y, de esta manera, mejorar la precision del sistema de posicionamiento. Finalmente se ha caracterizado el mecanismo paralelo de dos grados de libertad, disenado para aplicaciones de metrologia y procesos de maquina-herramienta, utilizando una maquina de medir por coordenadas. La caracterizacion desarrollada del mecanismo permitira determinar los parametros geometricos en la fase de calibracion del mismo, asi como desarrollar, posteriormente, procedimientos de correccion en funcion de la precarga necesaria para aumentar la precision del sistema.