Method and apparatus for the measurement of plant density for the control of harvest machines

In a harvest machine of a type having harvesting tools at the front end thereof for cutting plant growth as the harvest machine moves forward, the harvesting tools emitting ultrasonic noise signals, the improvement of noise insensitive apparatus for measuring the density of plant growth in a cutting area in front of said harvesting tools and for controlling the forward movement of the harvest machine is response to the measured density, the apparatus comprising:

• transmitter means for transmitting an intermittent beam of frequency modulated ultrasonic pulses through said cutting area in a direction transverse to the forward direction of travel of said harvest machine, the transmitted ultrasonic pulses being deflected and absorbed by plant growth in said cutting area;
• absorption receiver means disposed opposite said transmitter means and operable to receive signals for a particular period following an acoustic time delay after each of said ultrasonic pulses is transmitted, the acoustic time delay and particular period defined to allow said receiver to receive the ultrasonic signal pulses of said transmitter means that pass through the plant growth in the cutting area;
• means for subtracting the noise signals generated during each particular period from the signals received by said receiver means during the particular period;
• reflection receiver means disposed forwardly and in a lateral spaced relation with respect to said absorption receiver means for receiving the ultrasonic pulses of said transmitter means that are reflected by the plant growth in said cutting area out of a transverse line between the transmitter means and the absorption receiver means;
• and
• means for evaluating the intensity, time delay and/or phase position of the ultrasonic pulses received by said absorption receiver means and said reflection receiver means to generate a harvest machine control signal for controlling the forward movement of the harvest machine.