Virtual On-machine Measure System Of Numerial Control Machine Tool

A virtual on-machine measure system of CNC machine tool was designed to overcome the limitation of traditional measure method which is inefficient because of second clamping error. The system measures the profile dimension by installing trigger probe on CNC machine tool and developing matched measuring software. A virtual instrument which has geometry measuring function by combining the virtual instrument and on-machine measure technology was developed in this paper. The virtual measure instrument can reduce the intermediate operations and enhance the accuracy and reliability of on-machine measure.The access arithmetic of roundness, straightness and flatness error were studied firstly. After comparing the practicability and feasibility of all the arithmetic, roundness error and flatness error will be evaluated with least squares method, straightness error will be accessed with minimum zone method and least squares method, the minimum result will be taken for the access criterion. The error evaluation formulas were derived step by step.After introducing the composing and processing principle of the system, the on-machine measure system was designed as a whole. The function of measure instrument software was analysed base on the requirements of the system. The software was divided into five function modules and the software framework was confirmed.Base on the arithmetic researching and system designing, the trigger probe was chosen, and the system platform on CNC machine tool was built. The design process and method of measure instrument software was presented emphatically in this section. The graphics, custom macros, communication, data processing and measure simulation function modules were implemented. The instrument can measure eight items: the center and diameter of a circle, length or width, standard plane position, height or depth, centers'distance of two circles, straightness error, flatness error and roundness error. The measure resault will be presented after finishing measure.All kinds of error sources will effect the on-machine measure system precision were introduced in the forth part of the paper, especially the error from the trigger probe. Take the generation mechanism of trigger probe error for foundation, trigger force in different trigger range were analysed in this section. And then the equations of pre-travel in different trigger range were derived. The probe errors include pre-travel error, length error and eccentricity error. An error compensation method by characterizing trigger probe errors was presented. The errors from access arithmetic and compensation methods were presented as well.After all the analysis foresaid, the virtual on-machine measure instrument was test on a CNC machine tool. The tests indicated that the instrument fulfilled all the expected requirements and the repeat positioning precision of trigger probe, the geometric dimension measure precision were at a high level.The on-machine measure instrument is a successful attempt on virtual instrument applying in geometric measure. Experiment showed that the virtual measure instrument can realize high precision measure and make the on-machine measure more intelligent and more effective. The instrument can be expanded function easily.