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Resonant Frequency of Rotating Anode X-Ray Tubes

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M Shin

M Shin*, P Lillaney, W Hinshaw, R Fahrig, Stanford University, Stanford, CA

SU-D-218-3 Sunday 2:15:00 PM - 3:00:00 PM Room: 218

Purpose: To evaluate a new rotating anode X-ray tube from the resonant frequency point of view for stable and safe operation, and to validate a finite element model for insight into X-ray tube rotor dynamics and vibration.

Methods: The 3-dimensional FEM model of the X-ray tube motor has been developed using ANSYS and COMSOL. The resultant resonant frequency from the FEM simulation is substantiated by experiments. During deceleration of the X-ray tube, an accelerometer and a corresponding amplifier send the time domain vibration response to a spectrum analyzer which generates the power spectrum. In the frequency domain analysis, a peak signifies large vibrations at that frequency. To corroborate the FEM model, the resonant frequency of the motor assembly without the anode attached was also measured. Lastly, a rough estimate of the resonant frequency can also be observed in angular speed curves which are obtained utilizing a quadrature position sensor.

Results: The first mode resonance is expected at 20.3 Hz from the FEM simulation. This result matches closely with the peak at 22.2 Hz in the power spectrum and the location of the abrupt decreasing acceleration (slope) in the speed curve at 22 Hz. Without the anode, the FEM simulation result of 35.1 Hz is equal to the first peak at 35.1 Hz, and the angular acceleration is suddenly reduced at 34.4 Hz.

Conclusions: For image-guided interventional procedures using a hybrid system, the X-ray tube should create flux at various times requiring repeated acceleration and deceleration of the motor. Hence it is ideal that the resonant frequency is higher than operational speed, although alternatively the motor could accelerate through the resonant frequency quickly. Design improvements to modify the location of resonance of our motor assembly are underway using the verified FEM model.

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