Virtual brake system

1. A method comprising:

monitoring a signal indicative of an orientation of a downhole tool, in which the downhole tool orientation is monitored using a rotational sensor at a spindle;

selecting a desired downhole tool orientation;

actuating rotation of a spindle configured to provide rotational force to the downhole tool;

causing rotation of the spindle to cease when the signal indicates the downhole tool is within an error tolerance of the desired downhole tool orientation;

actuating advancement of the downhole tool;

while advancing the tool, monitoring the signal; and

while advancing the tool, rotating the spindle to maintain the downhole tool within the error tolerance of the desired downhole tool orientation.

2. The method of claim 1 in which the downhole tool orientation is monitored using a clock sensor at the downhole tool.

3. The method of claim 2 comprising:

comparing the downhole tool orientation as monitored by the clock sensor to the downhole tool orientation as monitored by the rotational sensor; and

correcting for error between the two orientations when rotating the spindle until the downhole tool is at the desired downhole tool orientation.

4. The method of claim 1 in which the desired tool orientation has an error tolerance is 0.5 degrees.

5. The method of claim 1 in which the error tolerance is fifteen degrees.

6. The method of claim 1 further comprising:

stopping advancement of the tool when the downhole tool orientation is outside the error tolerance of the desired downhole tool orientation.

7. The method of claim 1 further comprising:

selecting a desired drill path;

wherein the desired downhole tool orientation is selected in response to the desired drill path.

8. An apparatus comprising:

a frame;

a spindle supported on the frame;

a drill string having a first end and a second end, wherein the drill string is removably and rotatably attached to the spindle at the first end;

a downhole tool disposed at the second end of the drill string; and

a processor, configured to perform the method of claim 1 .

9. A method, comprising:

rotating a drill string with a spindle and advancing the drill string with a carriage;

selecting a desired orientation of the spindle, wherein the step of selecting the desired orientation of the spindle comprises:

determining a desired drill string path; and

planning steering steps having specific spindle orientations to maintain the drill string on the desired drill string path;

stopping the spindle at the desired orientation;

advancing the drill string without rotation;

monitoring a clock position of the spindle; and

rotating the spindle to the desired orientation when the difference between the clock position and the desired orientation exceeds an error tolerance.

10. The method of claim 9 further comprising:

detecting a clock position of a downhole tool disposed at an end of the drill string distal from the carriage.

11. The method of claim 10 further comprising:

using the clock position of the spindle and the clock position of the downhole tool, adjusting the desired orientation of the spindle.

12. The method of claim 9 further comprising:

rotating the drill string while advancing the drill string when the desired drill path is straight.

13. The method of claim 9 wherein the step of advancing the drill string without rotation is performed when the desired drill path is curved.

14. The method of claim 9 in which the error tolerance is three degrees.

15. A method for drilling a bore along a path, comprising:

monitoring a clock position of a drill bit by monitoring a clock positions of a spindle configured to rotate the drill bit;

advancing the drill bit with rotation to maintain a straight path;

advancing the drill bit while maintaining the drill bit in a desired orientation to deviate from the straight path; and

while advancing the drill bit to deviate from the straight path, rotating the drill bit when the difference between the clock position and the desired orientation exceeds an error tolerance.

16. The method of claim 15 further comprising:

monitoring a clock position of an orientation sensor located at the drill bit and comparing it to the clock position of the spindle to generate a drill string wind up value; and

using the drill string wind up value to correct error in the value of the drill bit clock position.

17. A method, comprising:

advancing a drill string with a horizontal directional drill, the horizontal directional drill comprising a spindle, a carriage and the drill string, the drill string extending from the spindle to a drill bit;

operating the horizontal directional drill with at least one motor;

monitoring a spindle position of the spindle with a rotational sensor;

stopping the operation of the horizontal directional drill at a stopped position;

storing the stopped position in a memory;

monitoring an actual position of the horizontal directional drill while operation of the horizontal directional drill is stopped to determine whether the difference between the stopped position and the actual position exceeds an error tolerance; and

operating motor when the difference between the stopped position and the actual position exceed the error tolerance to place the horizontal directional drill within the error tolerance.

18. The method of claim 17 wherein:

the motor drivers rotation of the spindle; and

the stopped position comprises a clock position of the drill bit.

19. The method of claim 18 wherein the operation of the horizontal directional drill comprises rotation of the spindle.

20. The method of claim 18 wherein stopping the operation of the horizontal directional drill comprises stopping the advance of the carriage.