Research On The Accuracy Analysis And Relevant Problems Of Lower-mobility Tripod Hybrid Machine Tools

Since the end of the last century, the Hybrid Machine Tools (HMT) has emerged as a new type of manufacturing equipment. By using HMT, it is easy to satisfy the requirements of multi-axis NC machining, assemble and measurement, so the HMT can be utilized to fabricate the parts with complex surface. Due to the merits of great ratio of stiffness to mass, fast response, module design and environment adaptability, developing excellent HMT has been to the one of the research trends in the machine tool domain. Furthermore, the lower-mobility HMT is the most attractable one.Although many people in the worldwide range have resorted to develop the HMT, and even to achieve a little progress, the current focuses of the HMT research are still on its design, try and error stages. In the P.R. China, although domestic scholars and designers have gotten some research fruits, there is still a great gap compare to the level of the developed countries. Through the study on the HMT, the error problem or the issue about the accuracy has been found to be one of the greatest difficulties. Nowadays, the accuracy of the HMT is still lower than the traditional precision NC machine tool, so there is still a long way to go.In this work, the error analysis has been conducted on two HMTs developed by Northeastern University with 3-TPT and 3-TPS type respectively, and the corresponding error compensation algorithms are discussed too. The main contents of this work are listed as following:(1) Based on the specialties of the 3-TPT and 3-TPS HMTs, the trajectories and workspace of them are analyzed. Their kinematics equations are derived, and their singularity and the dexterity are evaluated based on the operational degree and condition number of their Jacobin matrices. Hence, their kinematics performances and the error sensitivities are clarified.(2) Based on the independent principle of the error source, the error models and error transfer functions of the 3-TPT and 3-TPS HMTs have been developed. The influences of the error sources from the driving bar length, joint position, position and pose of the moveable platform are discussed. (3) The positional errors of the 3-TPT and 3-TPS HMTs are analyzed under the static machining condition. Their positional error models are developed. The variations of their positional error in the workspace have been found by the models and simulated based on the Virtual Prototype. Two agreements show good agreement, which can be used to verify the correctness of the model analysis.(4) The first period dynamic error analysis is performed on the 3-TPT and 3-TPS HMTs in order to discuss the effects of the thermal error and deformation caused by the dynamic cutting force. The research topics include the sources and modeling of the thermal and dynamic cutting force errors. The dynamic error analysis of the 3-TPT and 3-TPS HMTs are conducted in ADAMS.(5) The errors of the structural parameters are measured on the 3-TPT HMT prototype based on the positional error theory, and their effects to the position are obtained. Furthermore, the straightness, parallelism and repeatability are evaluated.(6) The error calibration models are built for the 3-TPT and 3-TPS HMTs. The parameter identification method is deduced based on the gene algorithm. The strategies of error compensation are studied, and the corresponding compensation approaches are proposed to the 3-TPT and 3-TPS HMTs respectively.The error analysis results on the 3-TPT and 3-TPS HMTs are meaningful to do the error compensation for them. The deeper research on the error variation and accuracy synthesis of the HMTs in the similar configuration can be conducted based on this work. However, due to the complexity and time variability of the HMT, there is still a long way to go in order to improve the machining accuracy of the HMT. The urgent and most important research focuses should be concentrated on the error control and real-time compensation.