Coordinate measuring machines : a modern inspection tool in manufacturing

Coordinate Measuring Machines (CMM) are flexible and universal dimensional measuring devices with the capability for full integration into a CIM information network. Developed as highly precise measuring machines for specially designed measuring rooms, today\u27s CMMs are more and more used in shop floor applications which is a hostile environment for a precise measuring tool. CMMs are offered in a variety of configurations and levels of automation. For the CMM buyer it is therefore essential to have an overview of the different types of CMMs and their subsystems before making a purchasing decision. To obtain reliable measuring results that are used for controlling and improving manufacturing activities, it is essential to know how accurate the machine can perform and which parameters can influence its performance negatively. The US-standard B89.1.12M-1990 and the German industry guideline VDI/VDE-Richtlinie 2617 for CMM performance testing are compared. Coordinate measuring technique offers solutions for all dimensional measuring tasks and has replaced most of the conventional measuring tools used in metrology. The most important issues of this technique as discussed in detail in this thesis

Design and development of a new large-scale metrology system: MScMS (Mobile Spatial coordinate Measuring System)

This thesis arises from the research activity developed at the Industrial Metrology and Quality Engineering Laboratory of DISPEA - Politecnico di Torino, on a new system prototype for dimensional measurement, called Mobile Spatial coordinate Measuring System (MScMS). MScMS determines dimensional features of large-size objects and has been designed to overcome some limits shown by other widespread measuring sets used nowadays, like Coordinate Measuring Machines (CMMs), theodolites/tacheometers, photogrammetry equipments, GPS based systems, Laser Trackers. Basing on a distributed sensor networks structure, MScMS can accomplish rapid dimensional measurements, in a wide range of indoor operating environments. It consists of distributed wireless devices, communicating with each other through radiofrequency (RF) and ultrasound (US) transceivers. This frame makes the system easy to handle and to move, and gives the possibility of placing its components freely around the workpiece. The wireless devices − known as "Crickets" − are developed by the Massachusetts Institute of Technology (MIT). Being quite small, light and potentially cheap (if mass produced), they fit to obtain a wide range of different network configurations. These features make the new system suitable for particular types of measurement, which can not be carried out, for example, by conventional CMMs. Typical is the case of large-size objects which are unable to be transferred to the measuring system area (because of their dimensions or other logistical constraints) and thus require the measuring system to be moved to them. In the dissertation the system is described exhaustively and characterized through practical experiments. Then, the system is compared to classical CMMs and the indoor-GPS (iGPS), an innovative laser based system for large-scale metrology. Finally, future directions of this research are give

An investigation of the measurement, fixturing, and trimming of large sheet metal parts

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (p. 171-174).Stretchformed sheet metal part production offers many challenges in process improvement such as increasing flexibility and part accuracy while decreasing cost and cycle time. The Reconfigurable Tooling for Flexible Fabrication (RTFF) project addresses these issues. This thesis investigates the measurement, fixturing, and trimming of large sheet metal parts. The objective of the thesis is to first present the current and alternative methods of three-dimensional measurement, fixturing, and trimming, especially for the RTFF project. Then, recommendations on the appropriate technology depending on the desired outcome can be made. Research show there are many potential technological changes that can be made to improve these current operations that encompass the sheet metal forming process. Three-dimensional shape measurement is investigated in detail. The current technologies are able to measure large sheet metal parts but have many disadvantages. A promising method of three-dimensional shape measurement is being researched and developed using laser speckle wavelength decorrelation. This method is still in development but initial results show that this method will decrease measurement time, decrease the amount of precision hardware needed, and decouple accuracy with the range of the object. Many of these factors are disadvantages of current measurement systems. A critical component of the promising measurement system is a precision linear actuator. A proposed design, consisting of cascaded solenoids and mechanical stops, is evaluated and shown to be unacceptable since commercial linear actuators perform the function more accurately and for lower cost.by David P. Sun.S.M

Study and Characterization of a Camera-based Distributed System for Large-Volume Dimensional Metrology Applications

Large-Volume Dimensional Metrology (LVDM) deals with dimensional inspection of large objects with dimensions in the order of tens up to hundreds of meters. Typical large volume dimensional metrology applications concern the assembly/disassembly phase of large objects, referring to industrial engineering. Based on different technologies and measurement principles, a wealth of LVDM systems have been proposed and developed in the literature, just to name a few, e.g., optical based systems such as laser tracker, laser radar, and mechanical based systems such as gantry CMM and multi-joints artificial arm CMM, and so on. Basically, the main existing LVDM systems can be divided into two categories, i.e. centralized systems and distributed systems, according to the scheme of hardware configuration. By definition, a centralized system is a stand-alone unit which works independently to provide measurements of a spatial point, while a distributed system, is defined as a system that consists of a series of sensors which work cooperatively to provide measurements of a spatial point, and usually individual sensor cannot measure the coordinates separately. Some representative distributed systems in the literature are iGPS, MScMS-II, and etc. The current trend of LVDM systems seem to orient towards distributed systems, and actually, distributed systems demonstrate many advantages that distinguish themselves from conventional centralized systems

Integrated inpection of sculptured surface products using machine vision and a coordinate measuring machine

In modem manufacturing technology with increasing automation of manufacturing processes and operations, the need for automated measurement has become much more apparent. Computer measuring machines are one of the essential instruments for quality control and measurement of complex products, performing measurements that were previously laborious and time consuming. Inspection of sculptured surfaces can be time consuming since, for exact specification, an almost infinite number of points would be required. Automated measurement with a significant reduction of inspected points can be attempted if prior knowledge of the part shape is available. The use of a vision system can help to identify product shape and features but, unfortunately, the accuracy required is often insufficient. In this work a vision system used with a Coordinate Measuring Machine (CMM), incorporating probing, has enabled fast and accurate measurements to be obtained. The part features have been enhanced by surface marking and a simple 2-D vision system has been utilised to identify part features. In order to accurately identify all parts of the product using the 2-D vision system, a multiple image superposition method has been developed which enables 100 per cent identification of surface features. A method has been developed to generate approximate 3-D surface position from prior knowledge of the product shape. A probing strategy has been developed which selects correct probe angle for optimum accuracy and access, together with methods and software for automated CMM code generation. This has enabled accurate measurement of product features with considerable reductions in inspection time. Several strategies for the determination and assessment of feature position errors have been investigated and a method using a 3-D least squares assessment has been found to be satisfactory. A graphical representation of the product model and errors has been developed using a 3-D solid modelling CAD system. The work has used golf balls and tooling as the product example

Traceable onboard metrology for machine tools and large-scale systems

Esta tesis doctoral persigue la mejora de las funcionalidades de las máquinas herramienta para la fabricación de componentes de alto valor añadido. En concreto, la tesis se centra en mejorar la precisión de las máquinas herramienta en todo su volumen de trabajo y en desarrollar el conocimiento para realizar la medición por coordenadas trazable con este medio productivo. En realidad, la tecnología para realizar mediciones en máquina herramienta ya está disponible, como son los palpadores de contacto y los softwares de medición, sin embargo, hay varios factores que limitan la trazabilidad de la medición realizada en condiciones de taller, que no permiten emplear estas medidas para controlar el proceso de fabricación o validar la pieza en la propia máquina-herramienta, asegurando un proceso de fabricación de cero-defectos. Aquí, se propone el empleo del documento técnico ISO 15530-3 para piezas de tamaño medio. Para las piezas de gran tamaño se presenta una nueva metodología basada en la guía VDI 2617-11, que no está limitada por el empleo de una pieza patrón para caracterizar el error sistemático de la medición por coordenadas en la máquina-herramienta. De esta forma, se propone una calibración previa de la máquina-herramienta mediante una solución de multilateración integrada en máquina, que se traduce en la automatización del proceso de verificación y permite reducir el tiempo y la incertidumbre de medida. En paralelo, con el conocimiento generado en la integración de esta solución en la máquina-herramienta, se propone un nuevo procedimiento para la caracterización de la precisión de apunte del telescopio LSST en todo su rango de trabajo. Este nuevo procedimiento presenta una solución automática e integrada con tecnología láser tracker para aplicaciones de gran tamaño donde la precisión del sistema es un requerimiento clave para su buen funcionamiento.<br /

Valukappaleiden parametrinen mallinnus ja laadunvarmistus

Even though 3D modelling and 3D scanning have been industry standards in casting design and measurement for a long time, casting tolerance standards still usually rely on complete definition of castings in 2D drawings and linear dimensional tolerances. ISO 8062-4, published in 2017, is based on a general surface profile tolerance instead of separate dimensional tolerances, thus forming a logical connection between 3D modelling, tolerancing and 3D scanning. As the contemporary 3D methods are prominently used, the outdated ISO 8062-3 should be replaced with the new standard in casting tolerance definition. In this thesis, possibilities to include casting tolerances in casting CAD models are examined. The aim is to create dependent but separate 3D models that depict the allowed minimum and maximum state of the casting as allowed by the casting tolerance. The benefits of these tolerance models are evaluated considering quality verification, strength calculations and collision detection. ISO 8062-4 casting tolerance and a traction sheave from an NMX hoisting machine are used for modelling case study. In addition, different measurement methods are reviewed to determine guidelines for casting measurement based on contemporary methods and standards. The case study revealed that tolerance model construction is difficult and time-consuming compared to the achieved benefits. Therefore, no implementation to every casting by default is recommended. Attention was also paid to modelling techniques and conventions that should be followed regardless of the tolerance models. 3D scanning should be utilised in casting quality verification because of its coverage, speed and ability to compare scanned 3D model directly to the nominal model. Measurement instructions were determined considering the requirements of ISO 8062-4 and the possibilities and restrictions of 3D scanning. An exemplary casting drawing of the traction sheave was created according to ISO 8062-4. Digital 3D product definition and 3D scanning were taken into account when determining the drawing indication.Vaikka 3D-mallinnus sekä 3D-skannaus ovat jo pitkään olleet vallitsevat suunnittelu- ja mittausmenetelmät valuteollisuudessa, valutoleranssistandardit nojaavat pitkälti vielä valujen täydelliseen esittämiseen 2D-kuvissa sekä lineaaristen mittojen tolerointiin. Vuonna 2017 julkaistu ISO 8062-4 perustuu yleiseen pinnanmuototoleranssiin yksittäisten mittojen toleroinnin sijaan, jolloin uusi standardi muodostaa ehyen ja loogisen jatkumon 3D-mallinnuksen ja 3D-skannauksen kanssa. Nykyaikaisia menetelmiä käytettäessä onkin syytä korvata vanhentuneisiin työkaluihin perustuva ISO 8062-3 uudella standardilla valutoleranssien määrityksessä. Tässä työssä selvitetään, miten valutoleranssin saa parametrisesti sisällytettyä valukappaleen CAD-malliin, jolloin erilliset mallit kuvaisivat toleranssin sallimia valun minimi- ja maksimitiloja. Minimi- ja maksimitilojen mallien hyötyjä arvioidaan laadunvarmistuksen, lujuuslaskennan ja törmäystarkasteluiden kannalta. Toleranssimallien luonnissa käytetään standardin ISO 8062-4 mukaisia toleransseja sekä malliesimerkkinä NMX-hissimoottorin vetopyörää. Lisäksi tarkastellaan eri mittausmenetelmiä, ja pyritään määrittämään suuntaviivat nykyaikaisiin menetelmiin ja standardeihin perustuvaa mittausohjetta varten. Tarkasteluissa havaittiin toleranssimallien mallinnuksen olevan työlästä saatavaan hyötyyn nähden, jolloin niiden sisällyttäminen oletuksena jokaiseen valuun ei ole järkevää. Tarkastelun yhteydessä kiinnitettiin huomiota myös mallinnustekniikkaan ja tapoihin, joita tulisi valusuunnittelussa noudattaa riippumatta toleranssimallien käytöstä. Valujen mittaamisessa tulisi ensisijaisesti hyödyntää 3D-skannausta, jossa nimellistä CAD-mallia verrataan skannattuun 3D-malliin, ja joka kattavuutensa ja nopeutensa ansiosta onkin yleisesti käytössä valuteollisuudessa. Mittausprosessin kulku määritettiin samalla huomioiden standardin ISO 8062-4 vaatimukset sekä 3D-skannauksen mahdollisuudet ja rajoitteet. Malliesimerkkinä käytetystä vetopyörästä laadittiin ISO 8062-4:n mukainen valupiirustus, jossa huomioidaan myös nimellisen muodon määritys CAD-mallilla sekä 3Dskannauksen käyttö laadunvarmistuksessa

COMBINED NUMERICAL AND STATISTICAL MODELLING FOR IN-DEPTH UNCERTAINTY EVALUATION OF COMPARATIVE COORDINATE MEASUREMENT

Quality assurance at low cost needs a tight interaction between machining and inspection. For this reason, the modern view of quality control (QC) requires highly repeatable coordinate measuring systems (CMSs) capable of being integrated into the manufacturing process for in-process feedback. Using this method, it becomes possible to reduce scrap levels and production costs while increasing part throughput. CMSs such as coordinate measuring machines (CMMs) have been used for decades in traditional manufacturing industry to ensure that the size and form of a part conform to design specifications. Although CMMs are considered as powerful and accurate measuring systems, most can only maintain or guarantee their measurement capability in quality control rooms typically having environmental temperature control systems set to maintain a nominal 20°C and maximum variation typically limited to ±2°C.However, shop floor environments have significant variability in ambient temperature. The need in manufacturing for dimensional inspection on the shop floor has led to many technological advancements in manufacturing metrology during recent years. In particular, a recent development includes a parallel kinematic machine (PKM)-based automatic flexible gauge, which is the system under investigation for this thesis. In order to be able to determine the measurement capability of a measuring or gauging machine to dimension a part reliably, it is necessary to evaluate the measurement uncertainties. This thesis first employs the design of experiments (DOE) approach to implement a practical analysis of measurement uncertainty of the automated flexible gauge. Several experimental designs are applied to investigate the influence of various key factors and their interaction on the uncertainty associated with coordinate measurement in comparator mode, in which the geometry of a part is compared with that of a calibrated master part nominally of the same shape. The ISO 15530-3 method is applied to derive uncertainty budgets for the flexible gauging system. A comparison is then made between typical shop floor measurement methods namely hard gauging, on-machine probing (OMP) and the automated flexible gauge. A set of identical test pieces was manufactured and then measured repeatedly using each method, with process and operator variability added as necessary to include typical industrial conditions. The measurement uncertainty is then calculated and compared for each of the measurements. The results show the measurement uncertainty of the comparator technique, which are lower than would be expected from an absolute measurement under workshop conditions. Finally, Markov chain Monte Carlo (MCMC) methods are applied to evaluate uncertainty associated with comparative coordinate measurement using a more realistic probability model to avoid repeating measurements. Samples are drawn from the unnormalized posterior using Gibbs sampling. Another feature of this thesis is the developed empirical method based on Bayesian regularized artificial neural networks (BRANNs) for estimating point coordinates and associated uncertainties when no satisfactory measurement model can be developed and large experimental designs are not practical. The effectiveness of the proposed method is demonstrated using two case studies

Design and Applications of Coordinate Measuring Machines

Coordinate measuring machines (CMMs) have been conventionally used in industry for 3-dimensional and form-error measurements of macro parts for many years. Ever since the first CMM, developed by Ferranti Co. in the late 1950s, they have been regarded as versatile measuring equipment, yet many CMMs on the market still have inherent systematic errors due to the violation of the Abbe Principle in its design. Current CMMs are only suitable for part tolerance above 10 μm. With the rapid advent of ultraprecision technology, multi-axis machining, and micro/nanotechnology over the past twenty years, new types of ultraprecision and micro/nao-CMMs are urgently needed in all aspects of society. This Special Issue accepted papers revealing novel designs and applications of CMMs, including structures, probes, miniaturization, measuring paths, accuracy enhancement, error compensation, etc. Detailed design principles in sciences, and technological applications in high-tech industries, were required for submission. Topics covered, but were not limited to, the following areas: 1. New types of CMMs, such as Abbe-free, multi-axis, cylindrical, parallel, etc. 2. New types of probes, such as touch-trigger, scanning, hybrid, non-contact, microscopic, etc. 3. New types of Micro/nano-CMMs. 4. New types of measuring path strategy, such as collision avoidance, free-form surface, aspheric surface, etc. 5. New types of error compensation strategy