System and method for controlling a drilling machine

Abstract

A system and method for drilling a borehole using a drilling rig having a rotary drill bit includes monitoring one or more drilling parameters; determining whether the one or more monitored drilling parameters are within predetermined specifications for one or more of the monitored drill parameters; and, executing an exception control procedure for control of a drilling parameter. The exception control procedure receives an input sensor value associated with a drilling parameter and applies feedback control to establish a scaled error value that is used to compute a setting value for the drilling parameter. The drilling parameters controlled may include the rotation speed of the drill bit, the feed rate of the drill bit, the weight-on-bit, or rotation torque during retraction of the drill bit. A computer-readable database of specifications of drill bits may be provided as a part of the system.

I claim: 
     
         1 . A method for drilling a borehole using a drilling rig having at least one rotary drill bit, the rotary drill bit having a rotation speed and a feed rate, and a computer-readable database of specifications of drill bits; the method comprising:
 executing a procedure to regulate the rotation speed of the drill bit, the procedure comprising:
 executing a depth-of-cut (DOC) control procedure, where the DOC procedure receives an input sensor value representing the current feed rate of the drill bit; the DOC control procedure further:
 calculating a rotation speed target for the rotary drill bit for the rotary drill bit that is a function of one or more predetermined parameters obtained from the computer-readable database; and, 
 
 executing a control procedure to command adjustment of the rotation speed of the drill bit until the input sensor value matches the rotation speed target for the rotary drill bit. 
   
     
     
         2 . The method of  claim 1 , further comprising:
 executing an exception control procedure and outputting from the exception control procedure a command to reduce the rotation speed target when a predetermined jam prevention threshold is crossed.   
     
     
         3 . The method of  claim 1 , where the control procedure to command adjustment of rotation speed of the drill bit comprises a PIV procedure. 
     
     
         4 . The method of  claim 1  where the control procedure to command adjustment of rotation speed of the drill bit comprises a PID procedure. 
     
     
         5 . The method of  claim 1 , where an ideal depth of cut is calculated by steps comprising:
 looking up a cutting-tooth height for the drill bit in the computer-readable database; and,   multiplying the cutting-tooth height for the drill bit by a predetermined fraction.   
     
     
         6 . The method of  claim 5 , where the DOC control procedure calculates the rotation speed target by dividing the input sensor value by the ideal depth-of-cut.