Control system for controlling the displacement of a working portion of an implement

Claim 1

A control system for controlling the displacement of a working portion of an implement from a reference position, said reference position being the ground surface in the immediate proximity of said working portion and the displacement being the depth or height above the ground surface, comprising: (a) sensor means for determining the location of said reference position to provide a reference signal, said sensor means including a plurality of sensors, each adapted to be in the proximity of said working portion and each providing a sensor signal indicative of a reference position of the respective sensor, wherein said control system includes averaging means for producing said reference signal which is an average of all of said sensor signals, said reference signal being summed with a second reference signal to produce a modified reference signal which can represent an artificial ground surface point; (b) signal generating means for producing a displacement signal representative of a preselected displacement; (c) comparing means for producing an error signal proportional to the sum of said modified reference signal and said displacement signal minus a null point signal; and (d) servo means for controlling the displacement of said working portion to said preselected displacement thereby causing said error signal to be reduced to approximately said null point signal, wherein said error signal is amplified in a hysteresis amplifier to produce an amplified error signal, said hysteresis amplifier having a small gain when the value of said modified reference signal plus said displacement signal is in the neighborhood of the value of the null point signal, and the hysteresis amplifier having a larger gain when the value of said modified reference signal plus said displacement signal is outside the neighborhood of the value of said null point signal, to thereby produce a deadband symmetrical about said null point signal.