THESIS
2005
xiii, 71 leaves : ill. ; 30 cm
Abstract
Surface quality influences the objects performance in fields like wear, friction and assembly. All these factors can affect the quality of products considerably. Traditional contact or non-contact measuring methods such as stylus, SEM and AFM etc have been widely used in surface measurement for years. Nevertheless, there are some disadvantages of these instruments. For example, stylus has a finite radius, and therefore may not be precise. Furthermore, it may cause scratch on the surface. SEM and AFM instruments are costly....[
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Surface quality influences the objects performance in fields like wear, friction and assembly. All these factors can affect the quality of products considerably. Traditional contact or non-contact measuring methods such as stylus, SEM and AFM etc have been widely used in surface measurement for years. Nevertheless, there are some disadvantages of these instruments. For example, stylus has a finite radius, and therefore may not be precise. Furthermore, it may cause scratch on the surface. SEM and AFM instruments are costly.
In this thesis, a cost effective, high precision optical measurement system is developed for multiple applications. This precision instrument is leveraged on commercially available CD/DVD pickup head. The measurement results show that our system has a few advantages over the conventional stylus instrument. The focused laser spot is less than 1 micron in diameter, while the standard Profilometer has a finite stylus tip of 10 microns in diameter. Furthermore our system is a non-contact measurement technique which would not cause mechanical distortion of the measurement and would not damage the sample. Due to these differences, the measurement of standard Profilometer may not give the precise measurement results. Measurement has been made on a milled aluminium sample. There is 6-7X difference between the standard Profilometer and our system. Convolution analysis about 3X of the discrepancy is due to the difference in the sizes of the profiling mechanism. The remaining 2X may due to the mechanical deformation of the stylus on the measured surface. Therefore, our system can indeed be 6-7X more accurate than the conventional Profilometer which is widely used in industry.
The second application is for 3-D Profile Measurement. With the 3 dimensional PZT Actuators, objects with profile in millimetres can be measured precisely by non contact method. In comparison with the standard CMM machine, our system is low in cost. However, our system can only measure geometry of shallow features. Therefore it is not a replacement of more generally used CMM machine.
The proposed multi-purpose system can also be applied to the Lead Angle Measurement. The lead angle appears during the finishing of contact surface of rotary shaft, which may lead to early leakage or dry run. The precision of our optical system for Lead Angle is around a few hundredth of a degree. It is noted that the accuracy of lead angle measurement is limited by the geometric fluctuation or variation of the groove of the sample. Comparison to the existed thread method technique, our system is more precise and much more reliable.
Key words: Multi-Purpose, Optical Measuring System, CD/DVD pickup, Surface Roughness, 3-D Profile, Lead Angle
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