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COB587 CORREÇÃO DE ERROS SISTEMÁTICOS DE APALPADORES DE MÁQUINAS DE MEDIR POR COORDENADAS ATRAVÉS DA ANÁLISE DE FOURIER. / SYSTEMATIC ERRORS CORRECTION OF THE COORDINATE MEASURING MACHINES PROCESS THROUGH FOURRIER ANALYSIS
Olívio Novaski & André Luis Chautard Barczak
Departamento de Engenharia de Fabricação - UNICAMP - CP 6122 CEP 13083-970
CAMPINAS - SP - Brasil - E-mail: novaski@fem.unicamp.br
One of the most important sources of uncertainties in Coordinate Measuring Machines (CMM) is related with the probes, especially in manual CMM. These probes are mainly mechanical (touch trigger probe or TTP) and suffer from important systematic errors. Due to construction shape, these errors represent a large amount on the machine uncertainty. It is possible to make error corrections eliminating most of these systematic errors. This is not an obvious task, although it can be aided by computer techniques. In this paper a characteristic profile of the behavior of the probe is determined, through Fourier analysis, and it is used to correct the coordinates of the touched points. The measurement were done over a certified standard sphere of Perthen, and the CMM was a microval of the Brown & Sharpe. The final result could be improved up to 40% for circularity. This procedure can be used to other shapes, since one has standards of this same shape. Also the profile is determined for a probe and an equation can be stored for it. An exchange of the probe can be associated to this equation, making it easier to proceed to error corrections when more than one probe (or a setup of this probe) is available.
Keywords: Máquinas de medir por coordenadas, Análise de Fourier, Incertezas, Metrologia, Apalpadores eletro-mecânicos. / Coordinate measuring mchines, Fourier Analysis, Uncertanty, Metrology, Electro-mechanical process.
COB589 COMPARAÇÃO ENTRE UM ALGORITMO DE ZONA MÍNIMA DE TOLERÂNCIA E UM ALGORITMO DE MÍNIMOS QUADRADOS / COMPARISON BETWEEN A MINIMUM ZONE CENTER AND A LEAST SQUARE CENTER ALGORITHM
Olívio Novaski & André Luis Chautard Barczak
Departamento de Engenharia de Fabricação - UNICAMP - CP 6122 CEP 13083-970 - CAMPINAS - SP - Brasil
E-mail: novaski@fem.unicamp.br
The Coordinate measuring machine (CMM) became an important metrology tool in modern manufacturing. They can measure accurately and quickly improving automation conditions. Most of these machines still use least squares center algorithms to calculate circularity and other shape deviations. Recently the American Society of Mechanical Engineering (ASME) printed new Y14.5 and Y14.5.1 standards. They established definitively that minimum zone center (MZC) algorithms should be used instead of LSC ones. In the last years some MZC algorithms had been proposed. In this paper one of these MZC methods, the Voronoi algorithm, is compared with the LSC. The results show that the differences between the methods are negligible when using CMMs with higher uncertainties. However when using better CMMs (with smaller uncertainties), the differences are important.
Keywords: Metrologia, circularidade, mínimos quadrados, algoritmos, zona mínima de tolerância./ Metrology, Circularity, Lest squares center algorithms, Minimum zone center.
COB1007 FONTES DE ERROS NA MEDIÇÃO DA TEXTURA SUPERFICIAL COM ESTILETE E COM SONDA ÓPTICA / SURFACE TEXTURE MEASUREMENT ERRORS SOURCES WITH STYLUS AND OPTICAL PROBES
Lourival Boehs*, Luciano Bet** & Gustavo Renê Mostiack*
*Departamento de Engenharia Mecânica - Centro de Tecnologia - UFSC,
Caixa Postal 476 - 88040-900 - Florianópolis/SC - Brasil - E-mail: lb@grucon.ufsc.br
**Departamento de Engenharia Mecânica - Centro de Tecnologia - UFRN
Caixa Postal 1657 - 59072-970- Natal/RN - Brasil - E-mail: bet@leca.ufrn.br
Many different systems of roughness measurement are avaiable today. Although the modern instruments are very sophisticated, still exist many sources and kinds of error in surface texture measurement. Most important sources of errors are those related with the measurement instruments as well as the enviroment they are being used. Only stylus and optical follower instruments would be discussed here. These instruments represent one that are being used in most of the laboratories and industries that handle surface texture meaurement. Because of the growing interest in the relationship surface texture/technological function, it is vital to improve the methods in order to find out and eliminate the measurement errors or at least minimise their effects. The scope of this paper is to present the most important sources of errors in surface texture measurement and to propose ways to eliminate or minimize their effects in the measurement results.
Keywords: Surface Texture - Measurement - Stylus - Optical Follower - Errors / Textura Superficial - Medição - Estilete - Sonda Óptica - Erros
COB1157 TECHNIQUE FOR ASSESSING THE PERFORMANCE OF CO-ORDINATE MEASURING MACHINES (CMMs)
Joao Bosco de Aquino Silva
Departamento de Engenharia Mecanica, Universidade Federal da Paraiba
CEP 58100-000 Campina Grande, Pb, Brasil - E-mail: jboscona@terra.npd.ufpb.br
M. Burdekin
Department of Mechanical Engineering, University of Manchester Institute of Science and Technology, UMIST, UK
A new technique is proposed for assessing the performance of co-ordinate measuring machines(CMMs). This technique comprises a new form of space frame which has the form of a tetrahedron and is referred to as modular space frame as different configurations of tetrahedron can be obtained easily and rapidly. The modular space frame comprises magnetic ball links and a ball plate. The volumetric error data obtained when a CMM measures the calibrated modular space frame can be used to verify whether a CMM maintains the manufacturer specifications. The experimental results have demonstrated that the modular space frame technique has an acceptable repeatability and provides a practical and cost effective mechanical artefact for calibration, verification, periodic reverification and acceptance test of any type of CMM.
Keywords: Calibration; Verification; Co-ordinate Measuring Machines