Research On Error Modeling And Compensation Of High Precision Microminiature Machine Tool

With the widely use of micro parts in aerospace, nuclear industry, defense, automotive and medical equipment industries, its accuracy and complexity are increasing, so as to the requirements to corresponding manufacturing technology. As its features of high speed, precision, micro cutting force and a wide processing range, precision microminiature turn-milling has obvious advantages in field of complex micro parts manufacturing. However, there is lack of high precision microminiature machine tool aimed at the three-dimensional micro complex parts in current market. Research on geometric error and thermal error modeling of conventional turn-milling and five-axis machine tools has been maturing, but there is less study for precision turn-milling machine tools, and can not meet the growing demand for sophisticated microminiature parts.This research designed a high precision microminiature turn-milling machine tool used for manufacturing complex microminiature parts, based on the microminiature turn-milling techniques and macro-micro combined error compensation technology. Theoretical calculations, finite element simulation and experimental validation approach are adopted to study major error factors affecting the accuracy of the machine tool. The main contents and conclusions are as follows:(1) In order to fulfill the processing needs and equipment demands for complex three-dimensional microminiature parts, overall design work of high-precision microminiature turn-milling machine tool is completed. Determine the XYCTZB structure of the machine tool according to the theory of topology, function and precision requirements. A hydrostatic spindle is used as turning spindle, and a high-speed ceramic ball bearings spindle is used as milling spindle; a high-precision direct drive turntable is used as B-axis; a high-precision two-dimensional piezoelectric stage is used as micro drive, and the macro-micro combination movement system is designed to achieve two-dimensional error compensation; combination of air spring and inert marble block is used as isolation system, and can cut most of the external environment vibration; open mode of "PC + Turbo PMAC" control system is designed to achieve compensation control.(2) For geometric errors affecting machining accuracy, establish the error modeling for three different structure of high-precision microminiature turn-milling machine tool, according to the theory of homogeneous coordinate transformation. Comprehensive error model was deduced, and validate the XYCTZB structure was reasonable. Error sensitivity analysis and identification of critical error source are completed, and identified the key elements of machine design errors, which can provide a theoretical basis for the realization of error compensation and control instruction correction after the machine tool developed, and can also provide a theoretical reference for future upgrade machine tools.(3) The thermal error of milling spindle was studied based on the theory of heat transfer and thermal deformation. Simulation for the temperature field and thermal deformation of the milling spindle was taken by finite element method. According to the simulation results, the spindle thermal error detection experiments were carried out respectively in the no-load and cutting conditions, while cutting heat under cutting conditions were detected. According to the experimental data obtained, thermal error modeling and forecasting of milling spindle were completed using the feature weighted naive Bayesian method. Weights of different characteristics were calculated by information gain method. Axial and radial error models of thermal deformation were established respectively under the no-load and cutting conditions with high accuracy. The predicted results show that the models have good predictive capabilities.(4) Usually, straightness error is not compensated in machining, and it affects the precision machining seriously. So two-dimensional macro-micro error compensation method is studied. First, a detection method for straightness motion error was proposed based on principle of plane mirror interference. Uncertainty analysis showed that in a small stroke measurement range, the method is superior to Wollaston prism interferometer-based approach. Then built a macro-micro experimental platform. In order to reduce the straightness error sources, a macro stage with adjustable slide rails was designed and experimentally verified. Two-dimensional compensation experiments for positioning error and straightness motion error of slide were carried out using a macro-micro strategy. Response time of micro-stage were tested under no-load and load conditions to verify the availability in the processing. Comprehensive compensation scheme for motion error and thermal error was proposed at last.