Abstract:
In order to control the sonde of an underground object, such as an underground boring tool, a predetermined sequence of rotation steps is applied to the object and that sequence is detected. The detection of the appropriate sequence causes the sonde to change its function, for example by changing the carrier frequency of the signal transmitted by the sonde on to change the data output sequence or transfer rate, or to change output power. While it is possible to use a single rotation step, the use of more than one step, with each step to be carried out within a predetermined time, reduces the risk of error.

Description:
This application is a continuation of Ser. No. 10/601,189, filed Jun. 23, 2003, now U.S. Pat. No. 6,980,123, which is a continuation of Ser. No. 09/504,833, filed Feb. 16, 2000, now U.S. Pat. No. 6,606,032, which claims priority to United Kingdom Application No. 9904010.7, filed Feb. 22, 1999, the disclosures of which are incorporated herein by reference in their entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to the control of an underground object. It is particularly, but not exclusively, concerned with the control of a sonde forming part of an underground boring tool. 
   2. Summary of the Prior Art 
   It is well known that if an underground boring tool generates a magnetic field, that magnetic field can be detected above ground by a suitable locator. An example of this is described in e.g WO96/29615 in which a solenoid on or in the underground tool generates a magnetic field which is detected to measuring locations. It is also possible, by modulating the magnetic field, to transmit information from the underground boring tool to the locator. Therefore, it is possible to have a sonde in which such field generation, modulation, etc is controlled. The sonde then makes it possible to transmit information from the underground boring tool to the locator. 
   In particular, it is possible for the sonde to transmit data representing the orientation of the underground boring tool. In WO96/29615, the boring tool incorporated a tilt sensor, and the sonde could then transmit the data from that sensor to the locator. Other sensors, such as roll sensors, may also be provided. 
   In such arrangements, the sonde generated a low frequency electromagnetic field (typically 8 to 30 kHz), which carrier is modulated to transmit sensor data. Such communication is thus from the sonde to the locator, and there is no direct communication from the locator to the sonde. 
   Normally, the carrier signal generated by the sonde is at a predetermined frequency. The locator is then controlled to detect that carrier frequency, and the modulations thereon. However, signalling between the sonde and the locator may be affected by interference from underground sources of electromagnetic radiation such as electrical cables, or the magnetic field distortion effects of buried metallic structures. Such interference effects are frequency dependent, and therefore it is possible that transmission between the sonde and the locator at a particular frequency may be greatly affected by such interference, whereas transmission at another frequency may not be affected, or affected much less. Of course, changing the carrier frequency may also affect the range of transmission between the sonde and the locator, battery life, etc, and therefore there is potentially a balance between these factors. If the operator of the locator finds that interference is a problem, the operator may decide that operating at another carrier frequency would be beneficial. However, in the existing systems, it is not possible for the operator to signal to the sonde to change frequency. 
   It would, of course, be possible to provide a suitable signalling path from the locator to the sonde by increasing the complexity of both the locator and the sonde. This would increase the size and cost of the sonde, which may not be desirable or practical for an underground boring tool. 
   However, existing underground boring tools are normally connected to their drive in a way which permits the drive to rotate the boring tool. Many underground boring tools have an axially offset slanted face which enables the boring tool to be steered so that it moves in the desired direction at any time. In order to detect this rotation, sondes associated with such tools include a roll sensor, information from which can be transmitted to the locator. In normal circumstances, the information from the roll sensor is used by the operator to control the direction of movement of the boring tool. 
   SUMMARY OF THE INVENTION 
   However, it has been realised in accordance with the present invention that if a predetermined rotation or rotation sequence is applied to the underground boring tool, a roll sensor can detect such rotation and the rotation may be treated as a command for the sonde. Thus, if the operator wants to signal to the sonde to change carrier frequency, a predetermined rotation or sequence of rotations is applied to the underground or inaccessible boring tool, detected by the roll sensor of the sonde, which sonde then determines the frequency change needed. 
   Although the present invention has been formulated with particular application to an underground boring tool, it is applicable to an control of an underground or inaccessible object in which a predetermined rotation or sequence of rotations is applied to that object, which rotations are treated as commands to signalling operations from the underground object. 
   Where there is a single rotation, the present invention may provide that a change in carrier frequency of a sonde in the underground boring tool may be triggered by a rotation which is different from that needed to trigger a change of the sonde to a state in which it does not generate electromagnetic radiation (a “park” state). Alternatively, if the sonde does not have such a park state, the change in frequency may be triggered by a single rotation. 
   It should be noted that the present invention is not limited to the case where the command triggers a change in carrier frequency but includes arrangements in which the command triggers other changes in functions of the sonde. 
   Preferably, a sequence of rotations is used to transmit a command, each rotation of which must be completed within pre-set time limits. The sequence is then chosen so that it will not occur during the normal operation of the boring tool. The use of a time limit for each rotation in the sequence of rotations significantly reduce the probability of the detection of a command during normal activities of the underground boring tool. 
   The present invention thus permits signalling to the sonde in an underground boring tool without modification to the boring tool or significant alteration of the features or the physical size of the sonde. In addition to altering the carrier frequency of the sonde, other features of operation, such as data output sequence, data transfer rate, or carrier output power may be controlled by signalling using the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic block diagram of an embodiment of the present invention; 
       FIG. 2  shows the underground boring tool of  FIG. 1  in more detail; 
       FIG. 3  is a block circuit diagram of the sonde of the boring tool of  FIG. 2 ; and 
       FIG. 4  is a block circuit diagram of the locator of the embodiment of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Referring first to  FIG. 1 , an underground boring tool  10  is driven from a drive means  11  via a drive shaft  12 . The drive means is arranged to move the boring tool  10  forward, but also to impart rotations to the boring tool  10 . The boring tool  10  has a slanted leading face  13 , and thus the orientation of the boring tool  10  affects the direction in which it will move. 
   The boring tool  10  contains a sonde  20 , which incorporates a roll sensor which can detect the axial orientation of the boring tool  10 . The sonde also includes means for generating a magnetic field, which generating means is controllable so that the magnetic field has a carrier frequency and a modulation means, thus the frequency may be modulated to transmit data from the sonde  20 . That magnetic field is detected by a suitable locator  30 . That locator  30  has means for signalling to a remote station  40 , which remote station is connected to the drive means  11 . It is thus possible for the operator of the locator  30  to control the movement of the underground boring tool  10  from the location of the locator, by signalling to the remote station  40 , which then controls the drive means to drive the underground boring tool  10  in a suitable direction. 
   The sonde  20  is normally battery-driven and therefore to extend the total number of hours the sonde  20  underground, it may have a power saving mode for times in which the sonde  20  is not required to transmit data. This is known as the “park” mode. In that park mode, the sonde turns off the electromagnetic transmission, and also any other circuits of the sonde  20  which are not used. In order to initiate the park mode, the boring tool  10  is rotated through a predetermined roll angle, which can be detected by the tilt sensor of the sonde  20 . When the roll sensor detects that such a rotation has occurred, and there has been no subsequent rotation for a suitable period such as 2 or 3 minutes, the sonde enters the park mode. When the sonde detects that predetermined rotation, it may trigger a display on the remote station  40  to indicate to the operator that it has received the command to change to the park mode after the predetermined delay, so that the operator can initiate another rotation if the park mode is not needed. The park mode is cancelled immediately a further rotation of the underground boring tool is detected by the sonde  20 . 
     FIG. 2  shows the underground boring tool  10  in more detail. The slanted leading face  13  is more clearly shown, and  FIG. 2  also shows that the boring tool  10  has a slot  21  therein to aid the radiation of electromagnetic signals from the sonde  20 . The sonde  20  is rotationally keyed to the rest of the boring tool  10  by a key  22 . 
   In accordance with the present invention, the underground boring tool is rotated through a predetermined angle a plurality of times. That predetermined angle may be the same as that needed to initiate the park mode, but this is not a problem provided the time interval between successive rotations is less than that needed to trigger the park mode itself. 
   If there are n steps in the sequence, the number of possible commands to the sonde  20 , in addition to the park command, is n−1. If the angle of successive rotations in the sequence is different from that needed to trigger the park mode, there would then be n possible commands, but it is convenient for the angles to be the same. 
   In such an arrangement, each rotation in the sequence must be completed within a suitable time, such as 60 s otherwise the command will not be recognised. This use of a time limit for each step to be completed significantly reduces the probability of a command being identified during normal activities of the underground boring tool  10 . 
   The ability to send commands to the sonde  20  by rotating the boring tool  10  in a suitable sequence of rotations permits an operator to change the operation of the sonde. For example, signalling between the sonde  20  and the locator  30  may be affected by conductors such as utility lines and pipes  50 ,  51  underground adjacent the boring tool  10 . The interference generated is often frequency dependent, and therefore a change in carrier frequency may reduce the interference of the signalling. Therefore, if the operator using the locator  30  finds that there is interference, e.g because particular signals from the sonde  20  are not detected, a signal may be generated via the remote station  40  to the drive means  11  to generate a command by rotation of the underground boring tool which causes the sonde  20  to change its carrier frequency. The operator may then determine if the interference is reduced, and then the sonde  20  continues to operate at that new frequency. If there is still interference, the operator may again trigger the sonde  20  to change frequency by causing another command to be transmitted to the sonde  20  by rotation of the boring tool  10 . Other commands may change data output sequence, data transfer rate, or the output power of the carrier signal. 
     FIG. 3  shows the electrical structure of the sonde  20  in more detail. The sonde  20  is powered by a battery pack  60 , which provides the input to a power supply module  61  which outputs regulated supplies for the circuits of the sonde  20 . The control of the sonde  20  is by a microprocessor  62  which receives inputs from a battery sensor  63 , a pitch sensor  64 , a roll sensor  65  and a temperature sensor  66 . The processor receives data representing the outputs of the sensor  63  to  66  and generates two outputs. One output controls a modulation unit  67  which encodes the data which the sonde  20  is to transmit, and the second output from the microprocessor  62  controls an output signal clock  68  which generates a carrier signal which is modulated by the output from the modulation unit  67  in an amplifier  69 . The signal from the microprocessor  62  to the output signal clock  68  determines the frequency or frequencies which that clock outputs to the amplifier  69 . The amplifier  69  then controls a solenoid  70  to generate electromagnetic signals in which the carrier signal from the output clock  68  is modulated by the output from the modulation unit  67 . 
   In this embodiment, it is preferable for the sensors to operate step wise and thus, as shown in  FIG. 3 , the battery sensor has four output levels, the pitch sensor determines the pitch plus or minus 45° in steps of 0.1°, and the roll sensor determines rotations in 12 or 16 equal sectors. Thus, the roil sensor permits a sequence of rotations to be detected, in order to send commands to the sonde  20  by rotating the boring tool  10  in a suitable sequence of rotations. If such a sequence of rotations generates a command which is identified by the microprocessor  62  as one involving change of the output frequency, a suitable change is applied to the output clock  68 . 
     FIG. 4  then shows in more detail a possible structure for the locator  30 . The locator has a detection coil  80 , the output of which is passed via a pre-amplifier  81 , a band pass filter  82 , and an adjustable gain amplifier  83  to a mixer  84 . The mixer  84  also receives an input from a frequency synthesiser  85 , the frequency of which is selected by a suitable input from the remote station  40  in a way which corresponds to the frequency of the carrier signal from the sonde  20 . Additionally, when the sonde frequency is changed, the locator frequency synthesiser  85  is also changed under control of the operator/computer so that the data can be received at the new frequency. The output of the mixer  84  is then passed via a band pass filter  86  and an automatic gain control amplifier  87  to a demodulator  88 . The demodulator  88  receives the signal from the automatic gain control amplifier  87  and passes it directly, and via a band pass filter  89 , to a mixer  90 , the output of which passes via a low pass filter  91  and a comparator  92 , to output data representing the data applied as a modulation to the carrier signal from the sonde  20 . That data output may then be passed back to the remote station  40 .