| A inertia mass block in a number of conventional instruments which based on inertial vibration measurement such as accelerometer, speedometer and displacement transducer must be connected with sensor shell rigidly fixed with vibration object measured using elastic elements. The vibration signals are acquired through inertia mass when the object measured vibrates. In this dissertation the inertial mass block in the inertial vibration measurment system is replaced by the magnetic levitation ball which is controlled by the magnetic force generated from helical coil. Using such kind of system has an advantage over conventional vibration measuring instruments because of non existence of mechanical connections and damping medium. Therefore, the system can easily measure the vibrations that comes from all the directions, or multi-dimensional vibration. The vibration measurement system designed has a wide range of applications than the traditional methods containing inertial mass block.The physical model consisted of the magnetic levitation ball, electromagnet, infrared emmiter/ receiver, PD controlled circuit had been set up. It is verified by vibration theory that the magnetic levitation ball vibration in the balance state can meet the second-order differential equations with constant coefficients like inertial mass vibration in the inertial vibration measurement system. In addition the natural vibration frequency of the magnetic levitation ball had been also definend by comparing the both vibration equations, which is concordant with that from the experiment. Therefore it can be shown from theoretical and experiment that the using magnetic levitation ball to vibration measurement is feasible.In this dissertation a vibration measurement platform with the magnetic levitation ball as a main part had been set up. In the vibration measurement system the vibration signals with the different amplitudes and frequencies generated from standard exciter to driven the vibration table is acquired by a optical displacement sensor and is transformed to the virtual oscilloscope throwgh the data acquisition card and is displayed. It is kown from the vibration characteristics of the frequency, the amplitude-frequency and the phase-frequency that the natural vibration frequency and the acceleration are 19.83Hz and 526.38m/s2,.the measurement range, the sensitivity of the system and diaplacement are 20140Hz , 300mV/m·s-2 and 04mm respectiively. Compaered with the velocity sensor bought from the market, besides the superior of the three-dimention measurement these parameters are basically the same with them of the velocity sensor and can meet the needs of the test system requirements fully.In order to improve stability of the system, the chaos phenomenon of amplitude-frequency characteristics, phase-frequency characteristics and the power spectrum of the system had been simulated numerically using MATLAB in the case of the different installation location of the optoelectronic displacement sensor H0, initial position of magnetic levitation ball X0 and PD parameters. At the same time the transition process of the magnetic levitation ball from chaotic state to non-chaotic state is also simulated numerically using phase trace as chaotic criterion based on the concept of the single and the double attractor and the range of the parameters caused chaos phenmena is defined. Furthermore, the optimal parameters such as installation location of the displacement sensor, initial position of magnetic levitation ball and PD parameters of differential circuits are obtained.Finally, the application of magnetic levitation ball in two-dimensional and three-dimensional vibration measurements was experimentally studied. The results show that the two-dimensional vibration waveforms caused by the vibration from any direction can be measured and the location of the vibration source can be determined by data fitting. ;For the three-dimention vibration, the vibration wavefom in the X,Y and Z direction can be also measured., but the waveform reconfiguration is needed to improve further.The magnetic levitation vibration measurement method in dissertation is a new method of vibration measurement. By further improving, this method will have application prospect in the two-dimention and three-dimention vibration measurment and provides a new idea for improving inertial vibration measurement.
|
PDF Full Text Request