Speed control circuit for mechanical scan ultrasonic imaging apparatus

摘要

In an ultrasonic imaging apparatus of the type having a plurality of selectable modes of operation, a motor-driven electroacoustic transducer is steered in a sector field in a predetermined relation to a selected operational mode. The sector scan format of returning echos is converted to a line-by-line raster display format in response to line sync pulses. The number of line sync pulses generated per unit time interval is scaled by a factor of N/M, so that it corresponds to the number of pulses generated by the encoder during the same time interval, where N and M are integers which are variable as a function of the selected mode. Phase comparison is made between the pulses generated by the encoder and the scaled line sync pulses to generate a phase difference signal from which a speed control signal is derived for controlling the speed of the motor. Since phase comparison is made for all the pulses generated by the encoder, the resolution of motor speed control is increased with respect to the number of energy transmissions, eliminating blurred or distorted tomographic images.