Method Of Geometric Error Separation For Form-free Measuring Machine

Based on the “small deviation hypothesis” for precision parts, the Form-freemeasurement machine is a new one, where the measuring instrument can process themeasurement for dimensions and form tolerances without knowing the geometricalform, parameters, and precision positioning. It is required to achieve form-freemeasurement, so higher requirements for its accuracy is put forward for the machine.The geometric error are measured accurately, simply and fast in order to provideaccurate data for the error correction, so that the accuracy of the measuring machinecould be improved. In that reason it has very important significance to research on theseparation technologies.The geometric error of the Form-free measurement machine is analyzed. Areference coordinate system is created on the machine body, some sub-coordinatesystems are set on each saddle, the theoretical relationship of the measurementmachine between the geometric error and the measurement error is derived by thehomogeneous coordinate transformation method which provides a theory base for theerror measurement and compensation. Two fast and low cost methods to measure andidentify the original errors of Form-free300measurement machine are proposed toachieve rapid and repeatable error detections. one is nine threads measurement toseparate errors based on laser interferometer, the other is a new method to separateerrors based on Laser Tracer. By using a simulation software to simulate andexperiment the Separation algorithm for the new method, The simulation and theexperiment verify the feasibility and accuracy of the method, which is suitable forCMM in geometric precision detection. Using laser interferometer to measure singleaxis movement in nine different positions at the Form-free measurement machine, theexperimental data are processed to obtain geometric errors after separation. Then bythe comprehensive error correction model we can calculate the measurement error ofthe entire measurement space, besides, a preliminary error correction scheme ispresented at last.According to high accuracy error measure of Form-free measurement machine,error correction can enhances accuracy of the CMM further, and new method toseparate the geometric error not only can apply to Form-free300, but also can applyother CMMs.