We study the dynamic contact characteristics between the rotor and stator of a ringtype ultrasonic motor by measurement and simulation. First, we measure the tangential and normal velocities and displacements of the rotor/stator interface using a LDA (laser Doppler anemometer). It is especially suitable for our measurement since it directly measures the velocity with high precision. Next, we solve the dynamic contact problem of the rotor/stator interface by use of finite element analysis taking into consideration inertia! effects and replacing the ring by an equivalent straight model of the rotor/stator. The calculated tangential and normal displacements and velocities of the rotor/stator are in good agreement with the measured ones. The effect of inertia was studied by changing the density of the rotor in the calculation. When the rotor's density is decreased to produce smaller natural frequencies, the velocity fluctuation and the frictional loss increase.
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