Patent ID: 8371769

Claim:
A control for a machine that applies a material to a subgrade at a work site and pulls a floating screed having a screed plate over the top surface of the material behind the machine, said floating screed being attached to the machine by a tow arm at a tow point on said tow arm, the vertical height of said tow point being controlled by an hydraulic cylinder on said machine in response to a valve control signal applied to an hydraulic valve by a valve control drive, said screed determining the thickness of the material on the subgrade and being manipulated by adjusting the height of said tow point, comprising: a first sensor mounted on the floating screed for sensing three-dimensional position, a second sensor for sensing the pitch of said screed, a memory for storing a desired contour of the top surface of the material applied to said subgrade at said work site, a processor circuit, responsive to said first and second sensors and to said memory, for determining the height of the trailing edge of the screed plate and the movement of the screed over the top surface of the material, for deriving a height error value, and for providing an adjusted height error value to said valve control drive such that the tow point may be adjusted by a predetermined amount as said screed plate travels a predetermined minimum distance.