Research And Implement Of Constant Cutting Load Machining Control Method Based On Spindle Motor Current

Research of constant cutting load control in machining process of NC machine tools is of much academic significance and engineering importance. The hard core of this control method is to compensate random fluctuate of cutting load and make it invariable to some extent by adjusting machining parameters in time. However, one difficulty of implementing this control method is real-time extraction of cutting load, because direct on-line measurement of cutting load adopted usually is very difficult and unpractical in actual application; In addition, another difficulty of implementing this method is how to find the regulatory variable exactly. This thesis puts the stress study on the indirect cutting load acquisition method based on on-line measurement of spindle motor currents, and then proposes the direct reverse control strategy based on model, that is adjusting the servo speed directly so as to change the cutting load real time according to the relation model of motor currents and cutting dosage made in advance as well as the fluctuate of spindle motor currents measured real time. Thus, constant cutting load control in machining process of NC machine tools is implemented. With the application of this approach, it is not only able to improve cutting accuracy but also able to improve the efficiency of machining, as a result, machine tools'potential is exerted adequately. Also, the auto-protected function of tools is realized to some extent and security of the system is enhanced. The research fruit of this thesis is one of most important parts of National 863 project 'Intelligent Error Compensation Equipment of CNC Machine Tools'and the antetype of this control system has passed the check and won the accept of the 863 expert group. It includes mainly achievements as follow. Firstly, character extraction of spindle currents is studied. With the cutting load and the spindle currents lucubrated, extraction method of standard cutting load signal of stable cutting process is presented, which has been improved oriented to the dynamic cutting process and applied to control in machining. Secondly, constant cutting load control strategy is studied. This thesis puts forward the direct reverse control strategy based on model and makes many researches and analysis of the model and identification method of the object. After that, the control strategy has been applied to the system with the feasibility discussed. Thirdly, based on the study of this thesis, the constant cutting load control system has been developed and implemented, which is able to not only applied to control but also for the use of study , including a database subsystem of parameter manage. Finally, the performance of this system is testified by applying it to milling machining and the certificate for the system of MID-South National Center of Metrology has been attained.