A critical investigation into the accuracy of a parallel coordinate measuring machine

Labuschagne, P. (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The increasing demand for manufacturing high quality and high precision products implies that special methods are required to ensure the quality and precision of these manufacturing processes and techniques (Lin and Chen, 2001; Küng et al., 2007). As a result, coordinate measuring machines (CMM's) are widely used as a means of precision measurement and verification of quality control. Ordinary CMM's have matured in their technology, yet are still lacking in their ability to measure at a sub-micron level (10-9 m). Furthermore, existing systems with sub-micron accuracy have a limited measurement range and are extremely costly (Sudatham et al., 2016). The process of designing and manufacturing micro-coordinate measuring machines (CMM's) is kept as a "trade secret" by existing market suppliers (Bommakanti, 2012). This has a negative effect on micro-manufacturing companies, since quality verification through the use of costly speciality CMM's, proves to be disadvantageous (Kruth et al., 2002). Introducing a CMM that can achieve a measurement accuracy in the sub-micron level has shown evidence to be beneficial for the market of micro and nanomanufacturing systems (Wu et al., 2012). However, the lack of theory supporting the challenging design and research of CMM's present great challenges in manufacturing and commercializing these systems. This thesis endeavoured to investigate the accuracy of the current system developed by Rugbani (2014) to fashion improvements. Rugbani's (2014) system is unverified and does not yet achieve the desired accuracy. Therefore, investigating the accuracy of the CMM designed and manufactured by Rugbani (2014) provided useful insight into the current state of the machine. Furthermore, the Rugbani (2014) system illuminated accuracy influencing factors of the CMM such as the design, layout, and measurement equipment. The initial hypothesis envisioned improvements through temperature compensation. Therefore, the study endeavoured to improve measurement accuracy, perform baseline accuracy study on a calibrated artefact, and to incorporate and test thermal error compensation. However, in the course of the study, various fundamental design problems of the system were identified. This thesis details the measurement test that was performed to examine the accuracy state of the CMM. Post-processing of the measurement showed unfavourable results with the original calibrated parameters. These parameters were tweaked, however, the results did not improve. Further tests were initiated to simplify methods of calibration to sanction improved regulation of these parameters. The mentioned tests evidenced that: the machine required large displacements for the laser measurement to change significantly; the ratio of probe movement to laser measurement is 20:1 and the tetrahedron has a position settling error. The study recommends an investigation into design improvement of the CMM to address fundamental design problems.

AFRIKAANSE OPSOMMING: Die toenemende vraag na die vervaardiging van hoë gehalte en hoë akkuraatheid produkte impliseer dat spesiale metodes nodig is om die gehalte en presisie van hierdie vervaardigingsprosesse en tegnieke te verseker (Lin en Chen, 2001; Küng et al., 2007). As gevolg hiervan, word Koördinaat Meetmasjiene (KMM'e) wyd gebruik vir die meting van akkuraatheid en die verifikasie van gehaltebeheer. Tradisionele KMM'e het in hul tegnologie gevorder, maar ontbreek die vermoë om op 'n sub-mikronvlak (10-9 m) te meet. Verder, bestaande stelsels met sub-mikron akkuraatheid het 'n beperkte meting reeks en is uiters duur (Sudatham et al., 2016). Die proses van die ontwerp en vervaardiging van Mikro-koördinaat Meet Masjiene (KMM'e) word as 'n "handelsgeheim" deur bestaande verskaffers gehou (Bommakanti, 2012). Dit het 'n negatiewe uitwerking op mikrovervaardigingsmaatskappye, omdat kwaliteit verifikasie deur die gebruik van duur spesialis KMM'e, blyk nadelig te wees (Kruth et al., 2002). Daar is getuienis dat die gebruik van 'n KMM met 'n meetings akkuraatheid op 'n sub-mikron vlak voordelig is in die mikro- en nanovervaardiging stelsel mark (Wu et al., 2012). Die gebrek aan onderliggende teorie vir die uitdagende ontwerp en navorsing van KMM'e verteenwoordig groot uitdagings vir vervaardiging en kommersialisering van hierdie stelsels. Hierdie tesis poog om die akkuraatheid van die huidige stelsel wat deur Rugbani (2014) ontwikkel is te ondersoek met die doel op verbeterings. Rugbani (2014) se stelsel is ongeverifieer en bereik nog nie die gewenste akkuraatheid nie. Die ondersoek na die akkuraatheid van die KMM ontwerp en vervaardig deur Rugbani (2014) het nuttige insig verskaf na die huidige stand van die masjien. Verder, het Rugbani (2014) die bydraende faktore tot die KMM akkuraatheid verlig, soos die ontwerp, uitleg en sensore. Die aanvanklike hipotese het verbeterings deur temperatuur kompensasie voorgestel. Daarom, het die studie gepoog om die metings akkuraatheid te verbeter, basislyn akkuraatheidstudie op 'n gekalibreerde artefak uit te voer, en inkorporeer en toets termiese-foutkompensasie. Deur die loop van die studie was verskeie fundamentele ontwerpprobleme van die stelsel egter geïdentifiseer. Daarom, word hier basislyntoetse beskryf wat ontwerp was om die akkuraatheid van die KMM vas te stel. Naverwerking van die metings het ongunstige resultate getoon met die oorspronklike gekalibreerde waardes. Hierdie waardes was verander, maar die resultate het nie verbeter nie. Verdere toetse is onderneem om vereenvoudigde metodes vir die kalibrasie van hierdie parameters te ontwikkel. Die genoemde toetse het die volgende bewys: die masjien benodig groot verplasings vir die lasermeting om aansienlik te verander; die verhouding van aftasterbeweging tot laserverplasing is 20:1 en die tetraëder het 'n posisie-vestigingsfout. Die studie beveel 'n ondersoek aan in die ontwerpverbetering van die KMM om fundamentele ontwerp probleme aan te spreek.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106229
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