Patent ID: 7325634

Claim:
A drilling machine, comprising: a frame, a tower supported by the frame and including a drill string, two tracks for movement over the ground, at least four yokes interconnecting the frame and the two tracks, each yoke pivotably connected to the frame and connected to one of the tracks, a plurality of hydraulic cylinders, each hydraulic cylinder being extendible and retractable in response to an associated control signal and connected to the frame and to an associated yoke, a plurality of sensors, each sensor sensing a parameter indicative of force and generating an output signal representing that force, and a controller that receives the output signals from the sensors, determines a force deviation for each hydraulic cylinder, and generates the control signals for the hydraulic cylinders based on the force deviations, wherein each hydraulic cylinder is controlled to retract or extend when an associated force deviation is greater than a predetermined magnitude.