| Abstract [eng] |
The aim of this master’s thesis project is to create a prototype of a spindle unit bearing defect imitation system. The system being developed utilizes a hardware in the loop (semi natural) imitation approach that in theory enables the user to simulate different local defects located on the inner or outer race of a bearing without the need of damaging any of the machines mechanical elements, while still providing sufficient defect imitation results. Defect imitation system that utilize this method would allow for a cheaper and faster development of specific machine tool diagnostics and condition monitoring systems. For the purpose of creating the prototype a desktop lathe machine ТУ2 12-111-75 was selected and several local race defects in the bearing unit were physically modelled and researched. Depending on the way these defects influenced the general vibroacoustic environment special requirements were brought up to for the developed system. It was concluded, that because of high level noise in the lower frequency range of the signal spectrum, imitation would be valid only in the 4 to 9 kHz frequency band. The prototype system actuator would have to be able to produce at least 0,4µm displacement and the produced vibratory acceleration at 4 kHz should be at least 4.5m/s2. In addition, using the research data from physical defect simulation, an impulse model for producing specific bearing defect influence on the mechanical structure signals was created. The modeled signal would be converted into voltage through a computer audio devise by using a special MatLab Simulink application. The actuator needed for the task was calculated and produced to be a piezoelectric element stack consisting from 15 layers of 1mm thick ЦТС-23 piezoelectric 20 mm in diameter ceramic plates. The created bearing defect imitation system prototype was tested by trying to imitate earlier physically modeled local bearing race defects. The relative actuator and transducer position options were checked to identify the best one for transferring defect information, which was revealed to be a collinear distribution. In order to test the quality of defect imitation, a comparative criteria was introduced to compare and quantify the similarity in % of the real defect induced vibratory signal to the imitated alternative. Results have shown that the created imitation system prototype is able to adequately influence the overall vibratory environment of the machine in a way that a real defect would at frequencies from 4 to 9 kHz. The reached similarity criteria for the time series signals of the imitated and real defect models is 22 %. For the envelope time series a higher similarity rate of 75% has been detected, and for the spectrum of the enveloped signal, the criteria was as high as 91% for some of the defect options. Since the envelope spectrum is the most commonly used diagnostic parameter for bearing defects it is safe to say that the created imitation system prototype can adequately imitate some localized defect on the bearing race cases. It is also evident, that the proposed hardware in the loop method for imitating bearing defects is viable and should be further studied. |
