Virtual brake system

1 . A drilling system, comprising:

a drill frame;

a spindle assembly comprising:

a carriage movable along the drill frame; and

a spindle, supported on the carriage and coupled to a drill string, wherein the drill string includes a downhole tool at its terminal end;

a sensor configured to monitor a position of the spindle assembly; and

a controller to receive signals from the sensor and provide operational instructions to the spindle assembly; and

wherein the controller is configured to:

capture a desired position of the spindle assembly when a virtual brake mode is initiated;

receive the signals;

when in the virtual brake mode, detect a discrepancy between an actual position and the desired position of the spindle assembly using the signal;

in response to the discrepancy exceeding a predetermined tolerance, automatically adjust the position of the spindle assembly based on the detected discrepancy; and

without engaging a mechanical brake, maintain the desired position of the spindle assembly by continuously adjusting the position of the spindle assembly.

2 . The drilling system of claim 1 in which the position of the spindle assembly comprises a rotational orientation of the spindle.

3 . The drilling system of claim 1 in which the position of the spindle assembly comprises a position of the carriage along the drill frame.

4 . The drilling system of claim 3 wherein the sensor comprises a position capture sensor.

5 . The drilling system of claim 4 wherein the position capture sensor is configured to capture a desired position of the carriage on the drill frame.

6 . The drilling system of claim 3 in which the drill frame comprises a rack.

7 . The drilling system of claim 6 in which the controller performs the step of maintaining the desired position of the spindle assembly by commanding the carriage to move along the rack.

8 . The drilling system of claim 3 in which the position of the spindle assembly further comprises a rotational orientation of the spindle.

9 . A virtual brake system comprising:

a sensor, configured to detect a position of a spindle assembly, the spindle assembly carried on a drill frame by a carriage; and

a controller having a first mode and a second mode, wherein:

when the controller is in the first mode the controller performs steps comprising:

determining a desired position of the spindle assembly;

receiving an actual position of the spindle assembly from the sensor; and

automatically actuating a motor to maintain the spindle assembly in the desired position; and

when the controller is in the second mode, the controller does not actuate the motor to maintain the spindle assembly in the position.

10 . The virtual brake system of claim 9 wherein:

the sensor comprises a clock sensor; and

the position of the spindle assembly comprises a rotational position.

11 . The virtual brake system of claim 9 wherein:

the sensor comprises a carriage position sensor; and

the position of the spindle assembly comprises a linear position along a rack.

12 . The virtual brake system of claim 11 further comprising a thrust control joystick, wherein the controller is configured to remain in the second mode when the thrust control joystick is actuated.

13 . The virtual brake system of claim 12 further comprising an operator presence detection sensor configured to detect the presence of an operator at an operator station, wherein the controller actuates a friction brake when no operator is detected at the operator station.

14 . A method of using the virtual brake system of claim 11 comprising:

with the carriage, advancing a spindle, thereby advancing a drill string into a subsurface borehole;

ceasing advancement of the spindle; and

thereafter, placing the controller in the first mode.

15 . A method of using a virtual brake to control a drilling machine, comprising:

activating a virtual brake;

at the time the virtual brake is activated, detecting a captured position of a spindle assembly with a sensor;

monitoring an actual position of the spindle assembly without activating a frictional brake;

in response to a deviation from the captured position while the virtual brake is activated, automatically causing the spindle assembly to return to the captured position;

deactivating the virtual brake; and

thereafter, moving the spindle assembly from the captured position.

16 . The method of claim 15 wherein the captured position of the spindle assembly comprises a clock position.

17 . The method of claim 15 wherein the captured position of the spindle assembly comprises a linear position along a rack.

18 . The method of claim 17 further comprising:

detecting whether an operator is at an operator station; and

if the operator is not at the operator station, actuating a friction brake to prevent movement of the spindle assembly.

19 . The method of claim 17 further comprising:

while the virtual brake is activated, actuating a thrust control to move the spindle assembly from the captured position.