| Due to the high efficiency, low cost and the capability of processing a wide range of materials, mechanical cutting techniques for the microstructure and micro components have drawn increasing attentions. By adding an ultra-precision vertical linear motion system, the ultra-precision machine tool is capable of machining components of complex surface, large free-form surface molds and ultra-precision optical elements, which have a wide range of application values and promising propects. Because of the vertical linear axes parallel to the gravity direction, the ultra-precision vertical linear motion system suffers much stringenter load condition than horizontal linear axes, which challenges the structure design of ultra-precision linear motion system, the design of its key components, dynamic characteristics, error motion modelling and control system of the ultra-precsion vertical linear motion system. By now, the ultra-precision vertical linear motion system technology has become a constraining factor for the development of the domestic ultra-precision machine tool. Therefore, it is desperately necessary to study the ultra-precision vertical linear motion system technology in-depth.Based on the symmetry principle of ultra-precision machine design, the overall design of an ultra-precision vertical linear motion system is completed for a multi-axis ultra-precision machine tool. By a comparative analysis on the traditional configuration of hydrostatic guide, a novel type hydrostatic guide is proposed, which is characterized by a closed structure configuration and with pressurized oil supplied on the hydrostatic guideways. Additionally, a mathematical model of stiffness chain of the vertical motion system is established to analyze the influences of vertical axis driving eccentricity, counter-balancing position, hydrostatic oil film stiffness and hydrostatic guide geometry parameters on the quasi-static errors of the ultra-precision vertical linear motion system, quantitatively.Upon complement of the overall structure design of the ultra-precision vertical linear motion system, the paper focuses on the key components of ultra-precision vertical linear motion system – orifice type hydrostatic guide. A general Reynolds equation is firstly derived for the variable film thickness hydrostatic lubricating. The numerical solution model for the Reynolds equation is established by finite difference method(FEM). By the established mathematical models, the effects of the gravity field, design parameters of hydrostatic guide, structural elastic deformation, and temperature of lubrication oil on the static performance of hydrostatic guide with rectangular recesses are investigated, respectively. A dual iteration modification robust method for hydrostatic guide design is proposed, which takes the effect of multi-physic field, e.g. the structure deformation and the thermal effect into account. The hydrostatic guide parameters have been optimized based on the proposed robust design methodology.The dynamic model of the ultra-precision vertical linear motion system has been established. From the view point of ultra-precision vertical linear motion system damping, the theoretical models for hydrostatic guide of rectangular recesses are deduced. By a comparative analysis, the influences of structure stiffness, payload mass and contact surface induced by the oil film have been studied, respectively. By utilizing the Finite Element harmonic response method, the effects of different types of lubrication oil on the dynamic performance of the vertical linear motion system have been investigated.A geometric error model for hydrostatic slides, considering the three-dimensional profile error of hydrostatic guide, has been proposed in this paper. Geometric error models for hydrostatic guides with single pad and double opposed pads are deduced, respectively. Results show that the geometric error motion is influenced by the profile error in both the width and length directions of hydrostatic guides. Additionally, the oil film stiffness plays an essential part in the geometric error motion when a hydrostatic guide is composed of opposed pads. Experimental results show the method is effective for predicting linear motion error caused by components profile error. On the basis of these work, complementary guidelines on ultra-precision vertical linear motion system with hydrostatic guideway are given. Additionally, for the background of ultra-precision multi-axis machine tool development, the error propagation chain model for ultra-precision vertical linear motion system is established, which considers the effect of hydrostatic oil film error averaging effects. Using the model, the paper analyzes the influences of the assembly errors on the ultra-precision vertical linear motion system spatial position and orientation errors, which provides guidelines for the development of ultra-precision vertical linear motion system. |
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