Browsing by Author "Labuschagne, P."

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    A critical investigation into the accuracy of a parallel coordinate measuring machine
    (Stellenbosch : Stellenbosch University, 2019-04) Labuschagne, P.; Schreve, K.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering (CRSES)
    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.