Automatic control of backhoe digging depth

The method of operating a backhoe to move the digging edge of the bucket thereof along a path parallel to the desired slope of the bottom of the excavation and with the digging angle of the bucket being substantially constant with respect to said desired slope, said backhoe having a power-actuated outreach boom vertically pivotal about a horizontal axis and defining an Angle A with respect to the horizontal, a downreach boom pivotally secured to the free end of the outreach boom and power-actuated relative thereto to define an Angle B therebetween, and a digging bucket pivotally secured to the other end of the downreach boom and power-actuated relative to define an Angle C between the digging edge of the bucket and the axis of the downreach boom, comprising the steps of:

• (1) generating a first electrical signal continuously proportional to Angle B;
• (2) controlling the power actuation of the outreach boom, hence Angle A, as a trigonometric function of Angle B, the length of the outreach boom, and the length of the downreach boom;
• (3) generating a second electrical signal continuously proportional to the Angle A;
• (4) controlling the power-actuation of the digging bucket relative to the downreach boom, hence Angle C, as a linear function of the sum of Angles A and B;
• and
• (5) manually controlling the power-actuation of the downreach boom through a digging stroke, thereby varying Angle B.

Apparatus for controlling a backhoe to move the digging edge of the bucket thereof along a path parallel to the desired slope of the bottom of the excavation and with the digging angle of the bucket being substantially constant with respect to said desired slope, said backhoe having an outreach boom vertically pivotal about a horizontal axis defining an Angle A with respect to the horizontal, a downreach boom pivotally secured to the free end of the outreach boom to define an Angle B therebetween, and a digging bucket pivotally secured to the other end of the downreach boom to define an Angle C between the digging edge of the bucket and its pivotal axis on the downreach boom, comprising, in combination:

• (1) three power-actuating means respectively operating on said outreach boom, said downreach boom, and said digging bucket to vary said Angles A, B and C;
• (2) means for continuously generating electrical signals respectively proportional to said Angles A, B and C;
• (3) computer means for generating a signal according to the following equation:
• ##EQU3## where R1 equals the length of the digging boom,
• R2 equals the length of the downreach boom,
• S is the angle between the desired slope of the excavation and the horizontal, and
• K = R2 sin (A.sub.o + S + B.sub.o) - R1 sin (A.sub.o + S)
• where
• A.sub.o and B.sub.o are the measured values of Angle A and B at the beginning of the digging stroke;
• (4) circuit means for applying the signal generated by said computer means to the power-actuating means controlling the outreach boom;
• and
• (5) means for controlling the power-actuating means for said digging bucket as a linear function of the sum of said signals proportional to said Angles A and B, thereby determining Angle C.