Research On Measuring Technology Of Geometric Accuracy For Large-size Parts Of Heavy-duty Machine

As the workhorses for machinery parts, heavy duty machine tools’ accuracy is directly related to the quality of work performance machined parts and even equipment package quality and even equipment package. Accurate and efficient measure to the geometrical precision of the parts compositing the machine greatly improve the machining accuracy. As the main geometrical factors that influence the part shape, straightness and flatness are important factors to influence the precision and performance of the machine parts. For the measuring, all geometric quantities’ measurement can be traceable to the measurement of straightness, flatness and other geometric quantities. Aiming to enhance the measuring accuracy and measuring efficiency of the geometric accuracy of large-size parts, the research on some questions of straightness and flatness measurement is carried out.Different methods of measuring straightness are given in the <GB/T 11336-2004 Measurement of departments from straightness>, but it just points out that the size and the accuracy of measured parts should be concerned when it is related to the measuring interval especially on the large-size straightness measurement. In this paper, the author converts the calculation of measuring interval to the determination of the sampling period, through the analogy of the relationship between straightness measurement and extraction of signal. The paper gives a method for calculating straightness measuring interval based on Nyquist sampling theorem, providing a theoretical basis for the large-size straightness measurement. With MATLAB, the author compiles a software for data processing. At last, the paper gives experimental verification to verify the correctness of this calculation method.When measuring large-size straightness, the large measuring stroke will cause the increasing of the accumulated error and measurement uncertainty. This paper puts forward the stitching method in large-size straightness measurement based on contour stitching. Aiming to verify the result of the stitching method in large-size straightness measurement, this paper introduces the method for calculating the measurement uncertainty from the process of measurement and error evaluation, and compares the measurement uncertainty of different measuring methods. At last, the paper gives experimental verification to verify the correctness of this method.To measure the flatness of the large-size ring guideway in heavy duty machine, this paper introduces a measuring method——Annular tangent method. The principle of this method is similar to the straightness measurement with level. For the traditional method of data processing, there exists tedious calculation and effect from subjective, this paper put forward a fitting method based on genetic algorithm to draw the standard sine curve, and with the measuring curve, the flatness and installation error will be gotten. With MATLAB, the author compiles flatness calculation software for large-size ring guideway. At last, the paper gives experimental verification to verify the correctness of this calculation method.