Hole-diameter Dynamic Control System Research&Design Of Helical Milling Device

As a new hole-machining technology, helical milling has many advantages than conventional drilling, such as more stability, smaller cutting force, higher accuracy, longer longevity, etc. Thus, it is more and more popular in composite material machining field in advanced countries in the world. However, China develops much later and slower in helical milling technology. Actually, we are still in testing level. Therefore, it is of great necessity to contribute on our own helical milling device. After lots of attempts, the airplane digital assembly team in Zhejiang University invented a new kind of robotic helical milling automatic system, which adopts hollow torque motor to realize the radial offset dynamic adjustment of the spindle axis. This paper is just based on this system. Taken torque motor as the research object, a closed servo control system based on adaptive robust control theory was designed to restrain the harmful influence derived from the bias structure.Firstly, the paper refers to the importance of helical milling technology development, and takes a comparison between helical milling and conventional drilling, after which, the domestic and international developments are introduced. The advantages of adaptive robust control in nonlinear control fields and its real applications are also mentioned. In the last section of the first chapter, the main contents of the paper are introduced.Secondly, the paper pays attention to the brief introduction of the main structure and milling mechanism of the designed helical milling device, especially for the bias structure components, including structure analysis and force analysis. The dynamic model of the chosen torque motor is then constructed.Thirdly, based on the former analysis, the adaptive robust control methodology is selected for the design of bias structure’s close loop control system. Specifically, the gradient online adaptive method is used to erase the effect of modeling uncertainty; linear feedback is used to minimize the accuracy problem which caused by estimation error; the nonlinear robust feedback is added to minimize the bias structure error affected by the outer disturbance. Then, several Lyapunov functions are constructed to prove the rationality of the designed adaptive method and the stability of the designed control system.Fourthly, to fulfill the property index and function requirements, the control system scheme of the helical milling device and the application of MechaWare are determined. Then several experiments are designed and completed, including unmilling experiments, Aluminum Alloy material holes and laminated material holes machining experiments. The experiment results show that, when machining Aluminum Alloy holes with diameter of13mm,15mm and18mm, the hole diameter error (measured) can be controlled between-0.021mm and+0.021mm. Besides, when machining the stacked material holes, it effectively restrained the burr formation and delamination defects of the CFRP materials.Finally, the whole research work of the paper is summarized, the insufficient parts of the research are mentioned, and the future work is put forward.