Automatic control device for tractor mounted tools

An improvement in a tractor mounted tool having a power operated tool positioning mount and a control circuit therefor which includes a depth control circuit having depth sensor means for detecting vertical displacement of the tool and generating an output signal in proportional relationship with the instantaneous position of the tool, a depth selector means connected in the depth control circuit with the depth sensor means and having means for displaying a preselected position setting of the tool and generating an output signal in proportional relationship with the preselected position, a pitch control circuit connected in the control circuit with the depth selector means, the pitch control circuit including a pitch sensor means for detecting angular displacement of the tool and generating an output signal in proportional relationship with the angular position of the tool, and a pitch selector means connected with the pitch sensor means, and control means connected in the circuit, the improvement comprising:

• the depth and pitch control circuits each being connected together and each including a bridge connected voltage divider with the sensor and selector means of each circuit being a part of the bridge connected voltage divider associated with said each circuit;
• and
• the control means including null means connecting said sensor and selector means in each of said depth and pitch control circuits forming a null detector between each of said voltage dividers, a depth relay connected to a depth null means and a pitch relay connected to a pitch null means, said depth relay being de-energized when the potential difference between the depth sensor and the depth selector is below a triggering voltage of said depth null means, said control means of said depth and pitch control circuits each generating a control output signal when the sensor means output signal correspondingly compares with the selector means output signal thereby denoting that the power operated tool is at a preselected position, said pitch circuit control means being connected with said depth circuit and initiating a change in pitch of the tool when the tool is detected at a preselected depth.