Image Number 4 for United States Patent #4980871.
An ultrasonic tracking system comprising a transmitting unit and a drive unit. The transmitting unit is carried by the subject to be tracked and produces brief, periodic ultrasonic bursts. The drive unit has an ultrasonic receiver and a motorized assembly capable of tilting and panning an attached camera in response to control signals from the receiver. This receiver employs three ultrasonic microphones located at three of the four corners of an imaginary square centered on and perpendicular to the axis of the camera lens. The receiver measures the relative arrival times of signals received by the microphones, determines the direction and degree to which the camera is not pointed directly at the subject, and supplies control signals to the motorized assembly, to drive motors to re-orient the camera (and receiver) to point toward the subject.