Investigation of the effects of geometric factors on mechanical alignment system.

摘要

In this thesis, the geometric factors that affect the repeatability of multiple station mechanical alignment system have been investigated. The mechanical alignment method is commonly used in many industries because it is cheaper and easier to operate. However, very little systematic research has been conducted in this area so far and there are still some fundamental questions haven't been solved. Especially, most of the previous studies on the mechanical alignment system (MAS) have been carried out based on the application of single station machining process, in which deformation is the main concern. Those experience and theories can not be directly applied to other types of manufacturing processes, such as the LCD manufacturing process. The main concern of those processes is not the operating force for aligning a workpiece but the geometric factors and repeatability of multiple station process. Therefore, it is the aim of this thesis to investigate the effects of geometric factors, such as surface roughness and waviness, datum size and shape etc, on the repeatability of multiple station MAS.;In order to do the investigation, the simulation approach has to be used due to the complexity and difficulty of building a multiple station monitoring system. A theoretical method for generating the surface profiles has been proposed with the validation from real measurements.;A theoretical simulation model has been built to examine how surface roughness of the workpiece and datum can affect the repeatability of multiple station manufacturing processes using MAS. Our analysis shows that geometric consideration, a factor that has not been studied before, is extremely important for many multiple station applications. The level of alignment precision decreases as the level of surface roughness of the workpieces increases. Our analysis also shows that the effect of roughness on the repeatability heavily depends on the difference of the relative positions of the datum between different workstations.;A proper way to design the optimum datum geometry for the multiple station process has been presented in this thesis. Most of the previous works have considered mainly from the deformation point of view, and the planar shape datum was proposed as a mean of minimizing the effect. Our investigation shows that, planar shape datum, in the application where geometric factor is the main concern, could create serious problems like corner contact and multiple alignment position. Larger radius datum, to some extend, can also help to minimize the effect of surface roughness and waviness of the workpiece especially in the multi-step manufacturing process. However, as radius of the datums increase beyond certain range, the MAS becomes unstable. The corner contact of the datum and the existence of multiple alignment position can rapidly deteriorate the performance of the MAS. A discussion on how to design a proper size and shape of the datum is presented based on the consideration of workpiece imperfection and datum mis-setup.;The application of multiple station MAS in the current LCD type of manufacturing processes has been investigated. Some of the problems of the typical approach to use MAS have been identified. Due to these problems, the alignment variation in assembly process is beyond what the industries could tolerate. However, we found out that, by properly design and setup, the MAS with the mirror datum setup could significantly reduce the effects of workpiece imperfections and provide enough repeatability to meet the requirement of LCD industries.