An ultrasonic rotary encoder and its application to torque estimation

In this paper, the ultrasonic sensing of rotation angle, speed, and torque is proposed and successfully demonstrated. To generate a rotary encoder, an ultrasonic wave was sent to and reflected by the blades attached to a revolving shaft. The ultrasonic wave was amplitude-modulated by the blades and demodulated to a pulse train that represented incremental angles and revolution rates. The wave was also Doppler-shifted according to the rotation rates. The angular velocity was obtained by analyzing the frequency spectrum of the ultrasonic signal, and its time derivative yielded an estimate regarding the torque supplied to the shaft. The ultrasonic rotation sensing techniques were evaluated using a motor bench, and the measured data was found to be in agreement with the data obtained from the resolver and the strain-gauge torque sensor attached to the motor.