Patent ID: 8070385

Claim:
A control for a machine that applies a material to a subgrade and pulls a floating screed over the top surface of the material behind the machine, said floating screed being attached to the machine by at least one tow arm at a tow point on said tow arm, the vertical height of said tow point being controlled by a hydraulic cylinder on said machine in response to a valve control signal applied to a hydraulic valve, said screed determining the thickness of the material on the subgrade and being manipulated by adjusting the height of said tow point such that the top surface of the material follows a reference surface, comprising: a first sensor mounted on the machine, adjacent the front of the machine, for sensing the relative height of the reference surface and providing a first sensor output related thereto, a second sensor, mounted on said at least one tow arm adjacent said tow point, for sensing the height of the tow point relative to the reference surface and providing a second sensor output related thereto, a control circuit, responsive to said first sensor output and said second sensor output, for providing a valve control signal to said hydraulic valve for control of said hydraulic cylinder.