Geometrical error analysis of a CNC micro-machine tool

Previous years have been characterized by the growth of 3-D micro-components production. There is an alternative to manufacture micro-components by micro-machine tools and micro-manipulators using conventional mechanical techniques. In Mexico, several prototypes of micro-machine tools (MMTs) and micro-manipulators (MMs) have been developed. The principal characteristic of these prototypes is their low-cost, which influences in a reduction of their precision characteristics. For this reason, it is important to establish the MMTs error sources and to develop control systems that allow the MMTs operational characteristics to improve. The viability to use an adaptive control system to improve the operational characteristics of an MMT is reported in this paper. Employing this control system the MMT was able to manufacture a micro-shaft with 50 μm in diameter. Likewise, a method for geometrical errors analysis in MMTs is proposed. The method is based on the use of two-ball gages: one ball is employed as a probe (B1) and the other one as a reference ball (B2). By means of electrical contact, a database of several points of B2 placed in different positions is generated. Using this database, the sphere equation and the mathematical model of the MMT errors, it is possible to determine the center of B2 and the errors presented in the micro-machine moving axes by means of a genetic algorithm (GA). Using this algorithm, an average error in the MMT of 35 μm was determined and, by introducing a mathematical error model, it was possible to fit the experimental data to the theoretical data with an error of 6 μm. The information obtained from this algorithm can be employed in the development of control systems for low-cost MMTs.