An evaluation of cleaning methods for micro-CMM probes

Abstract

To support the manufacture of complex products made of multiple micro-parts, a traceable and accurate 3D-measurement system with sub-micron accuracy is required. This paper investigates the use of a micro electro mechanical system (MEMS) tactile-micro-probe for 3D-coordinate metrology on the micro-scale. It will show that probe-tip contamination may be a significant source of error for such tactile-probing systems. Even in a clean-room environment, there are many types of contaminants that may affect dimensional measurement accuracy. These mainly come from repeated contact between probe tip and artefact material. To address this issue a number of cleaning methods were utilized to remove contaminants from the MEMS tactile-micro-probe sensor. Scanning electron microscopy was used to assess the efficacy of each cleaning method. Initial findings on different cleaning methods including ultrasonic, plasma, micro-beam melting, electron beam melting and cryogenic cleaning have shown that the latter is a feasible process.

The Unpredictable Errors of Micro Tactile Metrology – Factors Affecting Stylus tip Contamination

“…The fragile nature of micro probe sensors makes effective cleaning of these devices a significant challenge. Initial work has been undertaken by the authors to investigate stylus tip cleaning methods and is described elsewhere [11], where a review of cleaning systems that were evaluated by use of SEM surface analysis to examine contamination on stylus tips following each cleaning process is presented. In addition a Clean Logix SP2000 snow-jet cleaning system was shown to remove particulate debris from stylus tips.…”

“…If the clean stylus tip is subsequently contaminated with debris during the probing operation, then there will be a possibility for errors to arise. Once the debris has been attached to the probe tip, any repeat measurements that coincide with this contact point on the sphere will result in a bias error approximately equal to the size of the contamination less any plastic or elastic deformation [11]. Based on this scenario a particle of just five microns in size may create a bias error that is 20 times greater than the expected system total uncertainty of 250 nm.…”

“…For example: dust or atmospheric contaminates such as pollen or other organic debris may contaminate stylus tips; loose debris such as particulates on the artefact surface from previous manufacturing processes may be picked up by the stylus tip during operation; the action of probing may result in micro surface wear releasing particulates to contaminate the stylus tip [4]- [6]. The debris will adhere to the tip's surface as a result of surface attraction forces which become a dominant force on the micro scale [7]- [11].…”

“…In previous work stylus tip contamination was addressed from a cleaning perspective; methods for stylus tip cleaning were investigated and promising methods for debris removal were presented [11]. However, this work did not investigate or quantify the likely timeframe during normal operation that would results in significant stylus tip contamination.…”

A microscopy approach forin situinspection of micro-coordinate measurement machine styli for contamination

“…Previous studies [1,10] have investigated the effectiveness of various cleaning technologies in removing contamination from µCMM stylus tips and have identified CO2 snow cleaning as an effective and safe technology to achieve this. Subsequently, a prototype snow cleaning device has been developed [11] by the authors for in situ cleaning of µCMM stylus tips.…”