Drill automation control system

A rotary blasthole drilling apparatus comprises a rotary blasthole drill and a drill automation control system. The apparatus includes a pull-down motor and a drill motor. The pull-down motor is driven by a pump to provide a pull-down force to a drill string, and the drill motor is used to provide rotary force to rotate a drill bit of the drill string. The drill automation control system includes a number of functional components including a user interface. Through the user interface, an operator sets a rotary torque set point that determines an amount of torque applied to the drill bit by the drill motor. The control system further includes a detector, for detecting pressure in the pump during a drilling operation, and a processor, which is operative under the control of a program stored therein and responsive to the rotary torque set point and signals from the pull-down pressure sensor for generating an error signal. The error signal is applied to a proportional control valve for modulating the pull-down pressure to provide a substantially constant torque to the system. The rotary torque set point may be varied as a function of one or more of the following external factors: excessive mast vibration, bit air pressure or bit plunge.