Method and apparatus of fine tuning the position of an ultrasonic sensor

Abstract

As disclosed herein, a new and improved method and apparatus provide for fine tuning the position of a servomotor used to drive a transducer mounted on an ultrasound probe to a desired position. This improvement is accomplished by processing the analog quadrature output signals of an incremental optical encoder, coupled to the servomotor. The improvement uses the positional information derived from the analog quadrature output signals. The analog quadrature output signals, defined as sine and cosine, are converted to digital square waves. The digital square waves are decoded to produce digital position quadrants, wherein each quadrant represents a specific motor position. The corresponding digital square waves are also decoded by a logic array device and coupled to the select input of an analog switch. The analog quadrature output signals are also coupled to an analog device that converts the output signals to four phase shifted sinusoidal wave forms, having a linear portion within a digital position quadrant. The select signals from the logic array device select one of the four phase shifted wave forms. The output of the analog switch is then compared to a reference signal. The resulting output from the comparison is an analog error signal. This analog error signal forces the motor towards the zero crossing within a digital position quadrant.