Paving machine control and method

A method of controlling a machine that applies a material to a subgrade 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, 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, said machine having a sensor for sensing the position of the screed forward of the trailing edge of the screed plate, comprising the steps of:

• sensing the height of the screed plate under the sensor and providing a tow point correction value,
• sensing the three-dimensional position of the trailing edge of the screed,
• determining the height of the trailing edge of the screed plate and the movement of the screed over the top surface of the material,
• storing a desired contour of the top surface of the material applied to said subgrade at said work site,
• comparing the desired height of the trailing edge of the screed plate with the determined height of the trailing edge of the screed plate as it moves over the top surface of the material and deriving a height error value,
• adjusting the height error value, and
• combining said height error value with said tow point correction value in accordance with the movement of the screed plate over the top surface of the material and providing the combined 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.

A method of controlling a machine that applies a material to a subgrade 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, 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 the steps of:

• determining the height of the top surface beneath a sensor ahead of the trailing edge of the screed plate,
• comparing the height of the top surface beneath a sensor ahead of the trailing edge of the screed plate with a design surface height to provide a tow point correction value,
• determining the height of the trailing edge of the screed plate and the movement of the screed over the top surface of the material,
• comparing the desired height of the trailing edge of the screed plate with the determined height of the trailing edge of the screed plate as it moves over the top surface of the material and deriving a height error value,
• adjusting said height error value, and
• combining said adjusted height error value with said tow point correction value in accordance with the movement of the trailing edge of the screed plate over the top surface of the material and providing a combined 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.