Earth working machine and blade condition control system therefor

An earth working machine having an earth shaping blade (30) employs a control system for maintaining the blade (30) at a desired slope relative to a reference grade irrespective of lateral movement of the blade (30) or deflection of front and rear frame sections (15, 18). A ground engaging trailing wheel (96) mounted at the rear of the blade (30) senses rotation of the blade (30) relative to the direction of machine travel resulting from rotation or lateral shifting of the blade (30) and operates a potentiometer (124) to produce a control signal proportional to the magnitude of blade rotation. A first pair of accelerometers (128, 130) mounted on the blade (30) for rotation by the trailing wheel (96) produces blade controlling signals respectively corresponding to the change in slope and pitch of the blade (30) relative to the front frame section (15) of the machine. A second pair of accelerometers (42, 44) mounted at transversely spaced locations on the front frame section (15) produce control signals indicative of the roll of the front frame section (15) while an additional accelerometer (90) mounted on the rear frame section (18) produces control signals indicative of the frame pitch. An electronic circuit (94) algebraically combines the control signals for use in controlling the operation of a pair of hydraulic cylinders (38, 40) which maintain the blade (30) at a desired slope.