Patent Publication Number: US-6668946-B2

Title: Backreamer

Description:
CROSS-REFERENCE TO THE RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/263,275 filed on Jan. 22, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to underground drilling machines. More particularly, the present invention relates to reamers for use in horizontal directional drilling. 
     BACKGROUND OF THE INVENTION 
     Utility lines for water, electricity, gas, telephone, and cable television are often run underground for reasons of safety and aesthetics. Sometimes, the underground utilities can be buried in a trench that is subsequently back filled. However, trenching can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, alternative techniques such as horizontal directional drilling (HDD) are becoming increasingly more popular. 
     A typical horizontal directional drilling machine includes a frame on which is mounted a drive mechanism that can be slidably moved along the longitudinal axis of the frame. The drive mechanism is adapted to rotate a drill string about its longitudinal axis. The drill string comprises a series of drill pipes threaded together. Sliding movement of the drive mechanism along the frame, in concert with the rotation of the drill string, causes the drill string to be longitudinally advanced into or withdrawn from the ground. 
     In a typical horizontal directional drilling sequence, the horizontal directional drilling machine drills a hole into the ground at an oblique angle with respect to the ground surface. To remove cuttings and dirt during drilling, drilling fluid can be pumped by a pump system through the drill string, over a drill head (e.g., a cutting or boring tool) at the end of the drill string, and back up through the hole. After the drill head reaches a desired depth, the drill head is then directed along a substantially horizontal path to create a horizontal hole. Once the desired length of hole has been drilled, the drill head is then directed upwards to break through the ground surface, completing a pilot bore. 
     The diameter of the pilot bore so constructed typically must be enlarged. To accomplish this, a reamer (sometimes called a backreamer) is attached to the drill string which is pulled back along the path of the pilot hole, thus reaming out the hole to a larger diameter. The reamer usually includes a reaming or cutting surface on which is mounted cutting teeth or other cutting or grinding elements. It is also common to attach a utility line or other conduit product to the reamer so that the product is pulled through the hole behind the reamer as the reamer enlarges the hole. 
     A backreamer, then, may perform several functions including: mechanically cutting, grinding and loosening the soil to enlarge the pilot hole diameter, directing drilling fluid to assist in the cutting action, mixing the loosened soil with the drilling fluid such that the resulting slurry is a consistency that will flow out of the bore when displaced by whatever product is to be pulled in, and transferring the longitudinal force required to pull the product through the hole. 
     The amount of torque necessary to rotate a backreamer depends on several factors which include: the outer diameter of the backreamer, the difference between the diameter of the pilot hole and the outer diameter of the backreamer, the type of soil, the speed at which the backreamer is being rotated, and the longitudinal force being applied to the backreamer. 
     When utilizing standard backreaming techniques a backreamer is pulled longitudinally along the path of the pilot bore. Under certain conditions, however, the backreamer may tend to deviate from the path defined by the pilot bore. For instance, typically the pilot bore and drill string lie in an arcuate shape. Therefore the longitudinal force being exerted on the drill string tends to straighten the drill string, especially when soil conditions require increased levels of force on the drill string. This straightening tendency can affect the location of the backreamer by pulling the reamer higher. In some jobs the backreamer may move as much as 12 to 18 inches from the pilot bore. Such inaccuracy can have negative effects particularly when a utility or natural obstacle such as a river is being avoided. 
     In other situations, where large diameter bores are being formed, the weight of the backreamer can cause deviation from the pilot bore. A backreamer is typically moved longitudinally along the pilot bore at a rate in proportion to the drilling fluid being pumped to the reamer and out of the pilot bore. Therefore, longitudinal progress may be very slow. A heavy backreamer in the right soils will tend to drop lower than the pilot bore as it rotates quickly but moves slowly longitudinally. 
     In still other situations, varying ground conditions can cause the backreamer to move. For instance where there are distinct strata of significantly varying types of soils, the transition zones between one strata and another can cause such a deviation. In another situation there may be random obstacles like relatively large rocks interspersed within soils, that likewise can cause significant deflection of the backreamer. 
     Deviation from the pilot bore during backreaming is especially problematic in applications where maintaining a desired grade is important. The installation of sewer lines is one such application. The forces exerted on the backreamer by the sewer line being pulled into the bore behind the backreamer as well as the forces exerted by the drill string to cut large diameter holes make it difficult to maintain the desired grade established by the pilot bore. Variations in soil conditions can likewise make it difficult to maintain the desired grade and hole straightness. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention relates to a backreamer adapted with an hydraulic cylinder for steering the reamer as it is pulled or pushed through a pilot bore. The hydraulic cylinder is coupled to both a carrier frame and a carrier frame housing so that by action of the hydraulic cylinder the carrier frame may be tilted relative to the carrier frame housing thereby increasing control and steering during the reaming process. 
     Another aspect of the present invention relates to a backreamer having an elongated carrier frame housing which operates to make deviation from the pilot bore more difficult. An increased ratio of length to diameter assists the backreamer in following the pilot bore and maintaining a desired grade. 
     Another aspect of the present invention relates to a backreamer adapted with two sondes for monitoring the position of both ends of the backreamer in order to assist in steering the backreamer by determining the orientation of the backreamer. One sonde is located at a proximal end of the backreamer, and the other sonde is located at a distal end of the backreamer. 
     Another aspect of the present invention is directed toward a method of backreaming which includes the steps of: providing a backreamer with an hydraulic cylinder which operates to tilt a reaming body or surface of the backreamer relative to a carrier frame housing of the backreamer; running an hydraulic line from a source outside the bore to the hydraulic cylinder; and operating the hydraulic cylinder to assist in steering the backreamer during the reaming process. 
     Another aspect of the present invention is directed towards a method of backreaming including the steps of providing a backreamer with two sondes, one placed at the proximal and distal ends of the backreamer and using the sondes to monitor the position and angle of the backreamer to assist in steering the backreamer and thereby maintaining a desired course along a pilot bore. 
     Another aspect of the present invention is directed toward including a laser sensitive guidance system within the backreamer to automatically and accurately guide the backreamer along a desired bore. 
     Another aspect of the present invention relates to a method for maintaining a desired grade for a backreamer along a pilot bore by guiding the backreamer with a laser beam directed along the desired grade and a laser sensitive target disposed within the backreamer. 
     Another aspect of the present invention relates to a backreamer adapted with a non-rotating carrier frame and rotating front cutting structure, a controller, a transducer capable of measuring mechanical deflection of the front cutting structure relative to the carrier frame, a steering system capable of directing the front cutting structure, a free motion connection with the product being installed into the ground, and a communication link to the drill rig. 
     Another aspect of the present invention relates to a backreamer adapted with a non-rotating carrier frame and a rotating cutting structure further adapted such that whenever the formed bore deviates from a straight cylindrical hole there is a measurable deflection of movement within the carrier frame and cutting structure. 
     Another aspect of the present invention relates to a joint between a carrier frame of a backreamer and a front cutting structure that allows the front cutting structure to shift into an eccentric position relative to the carrier frame such that the cutting structure will advance more aggressively into a direction of the material that is more difficult to cut. 
     A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an embodiment of a reamer with hydraulic cylinder according to the present invention. 
     FIG. 2 is a partial schematic view of a backreamer according to the present invention comprising a laser sensitive guidance system. 
     FIG. 3 is a schematic view of the backreamer of FIG. 2 in use according to the present invention. 
     FIG. 4 is a schematic view of a support structure for use in the method of laser guiding a backreamer according to the present invention. 
     FIG. 5 is a cross section of an alternative embodiment of a reamer according to the present invention. 
     FIG. 6 is a side cross section of the reamer of FIG.  5 . 
     FIG. 7 is a cross section of a reaming portion of the reamer of FIG.  6 . 
     FIG. 8 is a cross section of a housing portion of the reamer of FIG.  6 . 
     FIG. 9 is a cross section of a second alternative embodiment of a reamer according to the present invention. 
     FIG. 10 is a schematic view of a the reamer of FIG. 7 coupled to a product line and disposed within a bore about to encounter a discontinuity in the form of a rock. 
     FIG. 11 is schematic view of the reamer of FIG. 10 having struck a rock and having its reaming body pivoted into a tilted position by the rock. 
     FIG. 12 is a schematic view of the reamer of FIG. 11 after reversing the longitudinal direction of the reamer without reversing the product coupled to the reamer. 
     FIG. 13 is a schematic view of the reamer of FIG. 12 with the reaming body tilted into an aggressive cutting position. 
     FIG. 14 is a schematic view of the reamer of FIG. 13 being advanced to cut into the rock in the aggressive cutting position. 
     FIG. 15 is a schematic view of the reamer of FIG. 14 after reversing the longitudinal direction of the reamer. 
     FIG. 16 is a schematic view of the reamer of FIG. 15 after the reaming body is recentered. 
     FIG. 17 is a schematic view of the reamer of FIG. 16 advanced while in the recentered position. 
     FIG. 18 is a third alternative embodiment of a reamer according to the present invention. 
     FIG. 19 is a fourth alternative embodiment of a reamer according to the present invention. 
     FIG. 20 is a fifth alternative embodiment of a reamer according to the present invention. 
     FIG. 21 is schematic view of a backreaming system according to the present invention having a walk-over locator and a receiver/transmitter. 
     FIG. 22 is an alternative embodiment of a backreaming system according to the present invention including a product driver. 
     FIG. 23 is an sixth alternative embodiment of a reamer according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     With reference now to the drawings, a description of various exemplary aspects of the present invention will now be provided. 
     FIG. 1 illustrates a backreamer constructed in accordance with the present invention. This embodiment incorporates features disclosed in U.S. Pat. No. 6,585,062, which is incorporated by reference herein in its entirety. The reamer shown employs a planetary drive system which includes a drive shaft  3 , a sun gear  6  disposed on the drive shaft  3 , a carrier frame  8  rotatably disposed around the drive shaft  3 , planet gears  15  mounted on the carrier frame  8 , and a ring gear  17  on which is mounted a reaming surface or reaming body  19 . The reaming body or surface  19  grinds and cuts away dirt and stone in order to increase the diameter of the pilot bore. 
     The drive shaft  3  is configured to be coupled to a drill string  9 . The drill string  9  rotates the sun gear  6 , which engages the planet gears  15  which in turn rotate the ring gear  17  and, thereby, the reaming body  19 . The drill string  9  may be coupled to the drive shaft  3  by means of a u-joint  5  as shown in FIG.  1 . 
     The carrier frame  8  is slidably received by a carrier frame housing  20  so that the carrier frame  8  may be tilted relative to the carrier frame housing  20 . The longitudinal force of the drill string pulling the carrier frame  8  is transferred to the carrier frame housing  20  primarily at point  23  where the carrier frame housing  20  is coupled to the drive shaft  3 . The drive shaft  3  may be coupled to the carrier frame housing at point  23  by means of thrust bearings, not illustrated herein, as is known in the art. 
     An hydraulic cylinder  25  is coupled to both the carrier frame housing  20  and the carrier frame  8 . The hydraulic cylinder  25  acts to tilt the carrier frame  8  and therefore the reaming body  19  relative to the carrier frame housing  20 . Tilting the cutting body  19  relative to the carrier frame housing  20  assists in steering the backreamer and in maintaining a desired bore grade. A second u-joint  11  may be incorporated into the drive shaft  3 . U-joints  5  and  11  cooperate to allow flexibility and a greater range of angles at which the carrier frame  8  may be tilted relative to the carrier frame housing  20 . 
     The hydraulic cylinder is configured to be coupled to an hydraulic supply line. The hydraulic supply line may run through the product being pulled into the bore, or may even run between the product and the hole wall. 
     As shown in FIG. 1, the carrier frame housing  20  may be elongated, increasing the ratio of its length to its diameter. The increased length of the carrier frame housing  20  makes deviation from the pilot bore less likely by preventing the reamer from rising or falling away from the pilot bore. To achieve this effect the length of the carrier frame housing  20  may be made at least as long as its diameter. Preferably the carrier frame housing has a length to diameter ratio greater than 2 to 1 or even greater than 5 to 1. 
     The present invention may also include a mixing element or elements  27  for mixing drilling fluid with cuttings of stone and dirt to be displaced from the hole. The mixing element  27  may be disposed on the drive shaft  3  and may be shaped as a bar, a blade, a propeller, a rod or any other shape suitable for mixing the slurry. Mixing is more efficient at relatively fast spinning speeds. In the embodiment shown in FIG. 1, the planetary drive train allows the drill string  9  and drive shaft  3  to spin the mixing element  27  at a relatively fast speed to maximize mixing efficiency while the reaming body  19  on the ring gear  17  is spun at a relatively slow speed to maximize cutting efficiency and control. The action of the planetary gear train accomplishes this result. The same drill string powers both the mixing element  27  and the reaming body  19 , yet the two rotate at different speeds. For example, the ring gear  17  and the reaming body  19  may rotate at one half or one third the speed of the drill string  9  and the mixing elements  27 . 
     The carrier frame housing  20  may define one or more apertures  29  through which the slurry of drilling fluid and mud enters the carrier frame housing  20 . At its distal end  30 , the carrier frame housing  20  is configured to be removably coupled to a product line such as a sewer line, utility line, or other conduit or product to be pulled into the hole. 
     The present invention may also include a sonde or sondes for monitoring the position and orientation of the backreamer. A sonde transmits electronic positioning signals to a worker typically by way of a hand-held complementary receiving device. A first sonde  32  may be positioned near the reaming surface  19  in order to monitor the location of the reaming surface  19 . A second sonde  34  may be positioned near the distal end of the carrier frame housing  20 . By comparing the location of the first sonde  32  with the location of the second sonde  34 , the orientation of the backreamer may be determined. Based on this orientation information, a user is able to monitor the bore grade during the reaming process and is able to adjust the bore grade by steering the reamer. For example a user may steer the reamer with a hydraulic cylinder as is shown in FIG. 1 or any other steering means. 
     A backreamer according to the present invention may also be used in conjunction with a laser guidance system in order to maintain a desired grade. FIG. 2 is a backreamer  100  according to the present invention comprising an elongated carrier frame housing  120 . The carrier frame housing  120  is comprised of a front body section  119  and a back body section  121 . Hydraulic cylinders  123  and  125  couple the front body section  119  and the back body section  121  so that the front and back body sections may be tilted relative to each other. 
     Inside the carrier frame housing  120  is disposed a laser sensitive target  122  in close proximity to an alternator  124 . A controller  126 , battery  128 , hydraulic pump  130 , and valve  132  are also disposed within the carrier frame housing  120 . The backreamer carrier frame housing  120  is open at a back end  136  of the back body section  121 . 
     As shown in FIG. 3 a laser emitter  138  may be placed in a pit at one end of a pilot bore  140 . A beam of laser light  134  may be directed through the pilot bore  140  along a desired grade. As the backreamer with carrier frame housing  120  is pulled through the pilot bore  140  along the desired grade, the laser sensitive target  122  detects when the carrier frame housing  120  deviates from the desired grade as established by the laser beam  134 . By means of the alternator  124  and the controller  126 , the hydraulic cylinders automatically tilt the front body section  119  relative to the back body section  121  in order to steer the backreamer toward the correct grade. 
     The backreamer  100  may include a planetary drive system or a direct drive system  101  coupling the reaming surface  102  to the drill string  142 . The drive system may include a reversing gearbox. Unlike the backreamer depicted in FIG. 1, the backreamer according to FIG. 2 does not require mixing elements. Drilling fluid is directed through the drill string to the reaming surface  102  and then back up the pilot bore. 
     The backreamer may be coupled to a product line to be pulled into the bore while still using the laser guidance technique as long as the product is hollow so that the laser beam  134  is able to pass through the product&#39;s center to the backreamer. As shown in FIG. 4, a support structure  158  may be included in the pit to guide the backreamer  143  or product line into the pilot bore  148  in a correct initial orientation  144 . Once aligned in a correct initial orientation the backreamer and product line are pulled through the pilot bore  148  by the drilling machine  146  at the ground surface  150  being continuously guided by the laser emitter  152 . 
     An alternative embodiment of a backreamer  300  is illustrated in FIGS. 5,  6 ,  7 , and  8 . A second, similar, embodiment is illustrated in FIG. 9 as  300   a.  In the first embodiment the backreamer  300  includes a main housing section  310  and a reamer section  320 . The housing  310  is shown in more detail in FIG. 8, and includes an elongated cylindrical section  312  and a support structure  314 . The support structure includes a spherical surface  316 . The elongated cylindrical section  312  can include slots  318  to allow fluid flow from the outside to the inside of the elongated cylindrical section  312 . FIG. 9 illustrates an alternate arrangement of a cylindrical surface  316   a  and an elongated cylindrical section  312   a.    
     FIG. 7 illustrates the reamer section  320  which includes a reamer  322  that is fixedly attached to a drive shaft  324 . The shaft can be constructed from a solid shaft or tube. The shaft  324  is supported on one or more bearings  326  which are installed into frame  328 . Frame  328  includes a spherical surface  329 . FIG. 9 illustrates an alternate embodiment wherein the shaft  324   a  is supported in frame  328   a  which includes a spherical surface  329   a.    
     Looking again at FIG. 6, the resulting back reamer  300  is assembled with the spherical surface  316  of the supporting structure  314  cooperating with the spherical surface  329  of the frame  328 . In this manner the reamer section  320  is able to pivot around point  330 , which is the center of the spherical surfaces  316  and  329 . Likewise in FIG. 9 this alternate embodiment is designed such that the reamer section  320   a  pivots about point  330   a.  In both of these embodiments points  330  and  330   a  are located outside the main cylindrical section  312  and  312   a  of the housing  310  and  310   a.    
     Looking at FIGS. 5 and 6 the backreamer  300 , and in FIG. 9 backreamer  300   a,  further include positioning elements  332 . There are  2  such positioning elements located perpendicular to one another, as can be seen in FIG.  5 . They are further located at the same longitudinal position along the elongated cylindrical section  312  or  312   a.  The positioning elements are attached on one end to frame  328  and  328   a  and at the other end to the elongated cylindrical housing  312  or  312   a.  Like the hydraulic cylinder  25  in FIG. 1, the length of these positioning elements  332  can be extended or retracted. This variation in length will effectively cause the frame  328  or  328   a  to pivot around point  330  or  330   a  relative to the housing  310 . This will have the effect of changing the orientation of the axis of rotation of the shaft  324  and  324   a  relative to the axis of the elongated housing section  312  or  312   a.  The positioning elements  328  may be any of various extendable arms such as hydraulic cylinders, electric actuators, powered screws, pneumatic actuators or the like. 
     An additional feature of backreamer  300 , which could be included for backreamer  300   a  although it is not illustrated, is an element to tow the product  160  being installed. This embodiment utilizes a towing plate  334 . This towing plate  334  is fixedly attached to the elongated cylindrical section  312  in a variety of ways. The main requirements include that it can be easily inserted, and then easily removed yet securely fixed in use. The towing plate  334  further includes a tow bar  336  that is adapted to cooperate with a plug  338  such that the tow bar  336  can slide within the plug  338  between a position where an enlarged section  337  of the tow bar  336  contacts the plug  338 , as drawn in FIG. 6, and a position where the plug would contact the towing plate  334 . With this arrangement the back reamer can move a limited distance without movement of the product, as defined by the difference between the effective length of the tow bar  336  and the width of the plug  338 . 
     Plug  338  is configured as required to connect with the product  160  being installed. This connection will vary greatly, depending on the type of product being installed. The method of connecting the backreamer  300  to the product  160  will include first installing the tow bar  336  and tow plate  334  into plug  338 . The plug  334  is then installed into the product  160  and then that joint is secured in any reliable fashion, not a part of this invention. Once that is complete the tow plate is installed into the elongated cylindrical section  312  and secured in place. 
     The opposite end of the backreamer assembly  300  is then connected to the drill string  142  and the backreaming process begins. As described above for FIG. 4 a support structure  158  may be used to initially guide the backreamer along a straight path. FIGS. 10-17 illustrate one possible scenario wherein this invention is useful. In FIG. 10 a pilot bore  140  has been formed that is close to the desired final location. Backreamer has been started along a straight path. As long as the soil is relatively homogeneous the forces on the reamer  322  will be substantially balanced. The positioning elements  332  will be controlling the orientation of the reamer section  320  so that its axis is aligned with the axis of the housing  310 . 
     If however, a discontinuity such as a rock  141  is encountered, as illustrated in FIG. 10, the forces will become unbalanced and the reamer section  320  will tend to rotate about point  330 . This will cause the positioning elements  332  to be affected. There are many types of actuators that could be utilized for the positioning elements  332 . In this embodiment they are drawn as hydraulic cylinders. 
     There are many types of control sequences that could be utilized ranging from load sensing to automated, active control. If load sensing were implemented the relative loads exerted onto the positioning elements could be measured and displayed, as will be described later, such that the drill operator could monitor the progress. If the load becomes unbalanced, slowing the advance rate of the backreamer, and allowing the reamer  322  to more aggressively cut through the soils would tend to bring the load back to a balanced state, and thus to keep the backreamer on a straight bore. 
     An alternative method is illustrated. In FIG. 11 the backreamer  300  has struck the rock  141 , the positioning element  332 , a hydraulic cylinder, has allowed the frame  328  to rotate. The aggressiveness of the backreamer can be defined by the pressures at which the cylinder  332  is allowed to extend or retract. Additionally cylinders  332  could include transducers that are capable of measuring their extension such as a Linear Inductive Position Sensor LIPS Series  106  manufactured by Positek Limited. There are many other methods of measuring the location of the frame  328  relative to the elongated cylindrical section  312  of the housing. Once there is sufficient loading and measured travel of one or both cylinders  332  a signal can be generated and sent to the drill operator or the drill as will be explained later. 
     FIG. 12 then illustrates the condition where the drill operator has stopped advancement and reversed the backreamer  300  such that the plug  338  is now nearly contacting the towing plate  334 . A signal is then generated to inform the drill operator to stop reversing the backreamer. 
     In FIG. 13 the cylinder(s)  332  are controlled by a control system with the backreamer, as will be explained below, to compensate for this obstruction, rotating the reamer such that the initial cutting point  323  is advanced in the direction of the obstruction  141 . 
     The drill operator will then be cued to begin advancing the backreamer again and as illustrated in FIG. 14 the reamer  322  cuts into the obstruction  141 . The backreamer advances in this manner for a short distance. During this advance monitoring the forces on the two cylinders  332  will not be a true indication of whether the boring is advancing in a straight direction. Thus this advancement is limited to a short distance. As soon as the elongated section  337  of the towing bar  336  contacts the plug  338  a signal is again sent to the operator to stop advancement and reverse direction. 
     FIG. 15 illustrates the next position wherein the back reamer has been reversed until the plug  338  contacts the towing plate  334 . 
     At this point the cylinders  332  can be adjusted to bring the axis of the frame  328  back into alignment with the axis of the elongated cylindrical housing section  312  as illustrated in FIG.  16 . The operator can then be cued to begin advancement. 
     FIG. 17 illustrates the advancement of the backreamer wherein the relative forces on the two positioning elements  332  are again being monitored to assess the straightness of the bore. 
     In the foregoing description it can be seen that an obstacle was encountered, detected, the operator signaled, a correction made, a short correcting boring made, the backreamer reset, and the boring continues. This process will be repeated as frequently as necessary in order to bore a straight borehole. 
     FIGS. 18,  19  and  20  illustrate variations of the internal control elements possible with this invention. FIG. 18 illustrates a system wherein a main controller  400  receives input  402  from the positioning elements  332  regarding load and position. It also receives input  404  and  406  from switches  405  and  407  respectively regarding the position of the backreamer relative to the product  160  and subsequently can generate a control signal  408  capable of controlling the positioning element. In the embodiment shown this is an electrical signal to control a solenoid  410  that positions a directional control valve  412  that subsequently controls the hydraulic cylinder  332 . 
     The power for the hydraulic system can come from a variety of sources. In this embodiment there is a hydraulic pump mounted on the housing  328  and driven by main shaft  324 , with the drill string  142 . Many other alternatives could be implemented. 
     The main controller  400  further generates a control signal  416  that is communicated to a radio transmitter  210  that is capable of communicating with a receiver  212 . Receiver  212  further includes an acoustic transmitter that generates an acoustic signal utilized as communication link  208 . FIG. 21 further illustrates this communication link  208  terminating at receiver  214 . Receiver  214  receives the acoustic signal and generates a radio signal, communication link  216 , to receiver  218 . Receiver  218  then generates a stronger signal which is communication link  220 , back to the drill rig. In this manner the embodiment illustrated in FIG. 18 is capable of communicating to the drill rig. 
     FIG. 19 illustrates an alternative wherein the main controller  400  communicates to a transmitter  202  that is capable of transmitting a signal to the surface, communication link  204 . This signal  202   a  is received by a walk-over locator  200 , as is utilized in drilling the pilot bore and is known in the art. The walk-over locator is further capable of producing a signal that is communication link  206  back to the drilling rig. 
     FIG. 20 illustrates an embodiment wherein a wire or wire bundle  222  is installed into the product  160 , and the signal transferred through this wire to the transmitter  218  which can then communicate back to the drill rig via communication link  220 . In this embodiment the power necessary to drive the positioning elements may be provided through this wireline. 
     Each of these 3 embodiments is illustrated with a transmitter  202 . This transmitter can be a standard sonde that is capable of also measuring roll position of the backreamer and the inclination angle. In addition to the roll position and inclination measured by the traditional sonde, the tension being applied to the product  160  can be also be measured and transmit to the surface as disclosed in U.S. Pat. Nos. 5,833,015 5,961,252 incorporated herein by reference. An alternate technique for recording this type of information within a data storage device within the backreamer for access after completion of the bore is disclosed in pending, published US S/N 09/794,124 Publication No. US2001/0024597A1 herein incorporated by reference. Any of these techniques can be utilized to provide data in real time for improved machine control or only for limited access to provide verification of a successful installation. Additional parameters such as fluid pressure at the backreamer and temperatures may also be communicated and or recorded. The backreamer of this invention is easily adaptable to any of these additional capabilities. 
     FIG. 22 illustrates an additional improvement related to this invention. A product driver  500  is installed in the pit wherein the product  160  enters the bore hole. This product driver is capable of pushing the product, in conjunction to the backreamer pulling it. The action of the driver  500  needs to be coordinated with the movement of the backreamer. The signal  404  from the sensor  502  mounted to sense when the backreamer is pulling the product  160  can be utilized to generate as signal in a manner to engage the driver  500  whenever the backreamer is pulling the product, but to disengage it whenever it is not. In this manner the one switch is capable of adequately controlling the product driver  500 . 
     FIG. 23 illustrates another aspect of the claimed invention. FIG. 23 shows a backreamer  600  having a housing  610 , a reaming body  620 , a drive shaft  630 , a frame  640 , and a cylinder  650  coupled to the housing  610  and the frame  640 . Extension member  660  is coupled to the reaming body  620 . When the reaming surface impacts obstacle such as rock  680  the reaming body will experience an asymmetrical load which may result in a curved, non-straight bore path. Even in a backreamer which does not include a pivot for tilting the reaming surface relative to the housing, such an asymmetrical load may cause sufficient stress on the backreamer to tilt the reaming body  620  relative to the housing  610 . Sensor  670  is designed to detect and measure any such deflection or tilt of the reaming body  620  or drill string relative to the housing  610 . In the embodiment shown, extension member  660  remains coaxial with the reaming body  620  when the reaming body  620  experiences the load and deflection caused by rock  680 . Extension member  660  is a relatively long shaft. The length of extension member  660  exaggerates the movement of reaming body  620  relative to the housing  610 . Sensor  670  may then measure the deflection of extension member  660  relative to the housing  610  in order to detect asymmetrical loads or tilting of the reaming body relative to the housing  610 . Cylinder  650  may then be used to counteract the asymmetrical load or to pressure the reaming body  620  toward an aggressive cutting orientation. 
     The above specification provides a description of the present invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.