Abstract: A method and apparatus are provided for controlling the working depth of a bucket for an excavating machine having an outreach boom which is pivotally attached at one end to the machine, a downreach boom pivotally attached to the opposite end of the outreach boom, a digging bucket pivotally attached to the end of the downreach boom opposite to that to which the outreach boom is attached, and hydraulic power cylinders for moving the pivotally interconnected elements. A laser beam is projected at a reference height and a beam sensor mounted on the outreach boom of the machine detects the beam by means of a plurality of individual sensor locations. The angular orientation of the downreach boom relative to vertical is detected and a microprocessor controller connected to the beam sensor and the angle sensor repetitively defines, as a function of the angular orientation of the downreach boom, one of the plurality of individual sensor locations as an on-grade sensor location.

Abstract: This invention provides a method and apparatus for controlling the digging depth of the bucket of a backhoe or an excavator so as to move the digging edge of the backhoe bucket in a plane parallel to an overhead reference plane defined by a rotating laser beam. The detecting means for the laser beam is mounted on a medial portion of the downreach boom and the control of the position of the bucket is accomplished by moving the outreach boom of the backhoe relative to the supporting platform so as to maintain the detecting means on the downreach boom in a fixed relationship with respect to the reference plane defined by the rotating laser beam.