D. González-Madruga

Application of a Force Sensor to Improve the Reliability of Measurement with Articulated Arm Coordinate Measuring Machines

A study of the operator contact force influence on the performance of Articulated Arm Coordinate Measuring Machines (AACMMs) is presented in this paper. After developing a sensor capable of measuring the contact force applied by an operator, a ring gauge has been used to analyse the relationship between the contact force and diameter and form errors measured with the AACMM. As a result, contact force has been proved as one of the main factors influencing the AACMM performance. A probe deflection model based on the Finite Element Method (FEM) has been also proposed in order to obtain the AACMM probe deflection caused by contact force. This allows measurement correction by comparing them with reference values, specifically, a ring gauge. Experimental test results show a significant measurement improvement that minimizes diameter error. Finally, an uncertainty evaluation for the contact force sensor and AACMM measurements with and without probe deflection model has been carried out in order to validate the ability of the sensor and the methodology followed.

A new concept of feature-based gauge for coordinate measuring arm evaluation

Articulated arm coordinate measuring machines (AACMM or CMA) have conquered a market share in the actual dimensional metrology field, overall when their role implies the inspection of geometrical and dimensional tolerances in an accurate 3D environment for medium-size parts. However, the unavoidable fact of AACMM manual operation constrains its reliability to a great extent, avoiding rigorous evaluation and casting doubt upon the usefulness of external calibration. In this research, a dimensional gauge especially aimed at AACMM evaluation has been developed. Furthermore, the operator skill will be revealed through the use of this gauge. A set of geometrical features, some of them oriented to evaluate the operator and others the equipment, have been collected for the gauge. The proposed evaluation methodology clearly distinguishes between dimensional and geometrical tolerances (with or without datum references), whereas actual verification standards only consider the former. Next, quality indicators deduced from the measurement results are proposed in order to compare AACMM versus coordinate measuring machine (CMM) performance, assuming that CMM possess the maximum accuracy that AACMM could reach, because CMM combines maximum contact accuracy with minimum operator influence. As a result, AACMM evaluation time could be significantly reduced since this gauge allows us to perform a customized evaluation of only those specific tolerances of interest to the user.

Feasibility Evaluation of Photogrammetry versus Coordinate Measuring Arms for the Assembly of Welded Structures

The present paper studies the technical feasibility of Photogrammetry and Coordinate Measuring Arms (AACMM or CMA) for the geometrical inspection of welded pins used for the assembly of medium-sized sheetmetal structures. As a result of this evaluation it was found that the deviations (measurement recorded by the device minus the nominal value of the measurement) obtained by means of Photogrammetry and the CMA were equivalent. Moreover, the number of measurements found to be out of tolerance by both methods was statistically equivalent. According to our results both methods are feasible for performing the dimensional inspection of the position of the welded cylinders of the structure as they are able to distinguish measurements inside and outside of tolerance and are equally capable of detecting the data variance.

Sensor Prototype to Evaluate the Contact Force in Measuring with Coordinate Measuring Arms

This paper describes the design, development and evaluation tests of an integrated force sensor prototype for portable Coordinate Measuring Arms (CMAs or AACMMs). The development is based on the use of strain gauges located on the surface of the CMAs’ hard probe. The strain gauges as well as their cables and connectors have been protected with a custom case, made by Additive Manufacturing techniques (Polyjet 3D). The same method has been selected to manufacture an ergonomic handle that includes trigger mechanics and the electronic components required for synchronizing the trigger signal when probing occurs. The paper also describes the monitoring software that reads the signals in real time, the calibration procedure of the prototype and the validation tests oriented towards increasing knowledge of the forces employed in manual probing. Several experiments read and record the force in real time comparing different ways of probing (discontinuous and continuous contact) and measuring different types of geometric features, from single planes to exterior cylinders, cones, or spheres, through interior features. The probing force is separated into two components allowing the influence of these strategies in probe deformation to be known. The final goal of this research is to improve the probing technique, for example by using an operator training programme, allowing extra-force peaks and bad contacts to be minimized or just to avoid bad measurements.

Development of a Behaviour Curve for Quality Evaluation with Optoelectronic Profilometers

This work shows an experimental procedure aimed to generate a graph with the optimal roughness parameters in order to obtain the best roughness measurements of an optoelectronic profilometer. The optimal parameters have been determined taking into account the grade of agreement between the optical roughness values and the equivalent values of traditional contact devices. The working parameters of the optoelectronic profilometer are based on computational filters which are controlled by software working with a 3D stratified colour map (chromatic fragmentation of the white light). However, these parameters substantially differ from the usual contact profilometers that work with 2D roughness profiles (cut-off, evaluation length and contact stylus radii). This work pursues to find the optical profilometer parameters, and its values, that ensure the best quality measurement for a wide range of machining process and testing several ISO roughness intervals.

The Use of Virtual Circles Gauge for a Quick Verification of Portable Measuring Arms

Portable Measuring Arms or Articulated Arm Coordinate Measuring Machines (AACMMs) unique characteristics bring flexibility to the inspection task and allow outside laboratory measurements. However, still a few works study their metrological behavior, uncertainty or assessment. In fact, AACMM assessment involves time consuming and expensive processes mainly inherited from CMM field. A virtual circle gauge similar to ball bars and a methodology based on international standards are proposed in order to simplify the evaluation test. Additionally, two metrological laboratories have evaluated different AACMM models with this gauge. Also, two gauge lengths (distance between circles) have be included in this study. Results have proved that virtual circle gauges are suitable to evaluate AACMMs and tested the influence of distance between virtual circles.

A Wiki Collaborative Application for Teaching in Manufacturing Engineering

The interest of the present work is focused on the improvement of the students learning process through the use of a Wiki-like platform. In our research The Wiki was intended as a mean in order to make easier the learning project. During the academic year 2011/2012 the Area of Manufacturing Engineering of the University of Oviedo was involved in a project which aim was the creation of a Wiki. Nowadays this software is used as auxiliary material for other subjects that are given by the Manufacturing Engineering Area in those new Engineering degrees that have been created in order to adapt the studies to the requirement of the European Higher Education Area (EHEA). According to the results obtained by the students, it can be stated that the higher the mark of the students Wiki the better his/her mark in the exam is.

Management of Manufacturing Engineering Seminars in the Context of New Educational Trends

A methodology for seminars developing in manufacturing engineering is presented. Often, when planning similar seminars, it is noted that seminars have a very limited duration. A normal way to overcome this limitation is to prepare the seminar educational documents, at students disposal, before the seminar date. In this point, ICT tools used for virtual teaching, like eXe-Learning, become a significant advancement. However, in this paper is not only considered the elaboration of seminar materials for students, but also a whole educational strategy for seminars developing in manufacturing engineering is stated.

Surface roughness prediction from combination of cutting forces, turning vibrations and machining conditions using artificial neural networks

Nowadays the evaluation of surface quality of manufactured products continues being a very important task for the industry. One of the lines of research associated to this subject tries to predict the surface roughness using signal analysis, such as vibrations, in the machining process. Many researchers have proposed models for determining the roughness based on the cutting conditions or the cutting forces. As the surface roughness depends on many variables, in this work different statistical values of cutting forces, tool vibration values and machining conditions are considered together for predicting surface roughness of turned metallic parts using artificial neural networks. We have notice the best predictions have been obtained when force and cutting conditions were combined together. The absolute error values obtained have been always below to 1.28 and 1.11 μm when using the median and root mean square (RMS) as descriptors, respectively.

Reliability of Monitoring Signals for Estimation of Surface Roughness in Metallic Turned Parts

Current trends in machining processes are focused in three goals: to increase the productivity and the reliability and to minimize costs. In this context, the development of signal monitoring systems is of vital importance for surface roughness inspection. One of the research lines associated to this context is oriented to predict surface roughness using indirect signal analysis, such as cutting forces or vibrations in the machining process. This paper analyzes the results obtained when comparing different nature signals combined with cutting parameters. The final goal is to quantify the deviations obtained with different monitoring signals for establishing the best ones to use as roughness evaluators. The best predictions were obtained when force and cutting conditions were combined together. The absolute error values remains always below 1.28 and 1.11 µm when using the median and root mean square (RMS) as descriptors, respectively.