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FIELD OF THE INVENTION 
     This invention relates to an earth borer system with a frame incorporating a movable rotary drive for a drill rod assembly consisting of at least two drill rods which can be detachably connected with one another, with a drill rod magazine mounted on the frame, with a release mechanism located on the frame which is provided with a clamping unit that engages in a first drill rod and a break-away unit that engages in one section of the said rotary drive or in a second drill rod, and with at least one transport arm attached to the frame which can move a drill rod released from the drill rod assembly into a standby position in the drill-rod magazine or take a drill rod from its standby position and position it on the drill rod assembly. 
     BACKGROUND OF THE INVENTION 
     An earth borer system of this type has been described earlier for instance in the publication EP-A-0 819 820. It includes drill rods which can be screwed together to extend the overall drill rod assembly. For drilling a bore hole, an additional drill rod is moved out of the magazine with the aid of the transport arm, attached to the drill rod assembly, screwed at one end to the rotary drive which for that purpose is retracted into a rearward home position, and screwed with its other end to the back end of the drill rod assembly. In analogous fashion, when upon completion of the drilling operation the drill rod assembly is withdrawn, the drill rods are unscrewed from the rear and the transport arm then moves them back into the magazine. 
     During the drilling process, the threaded junctions at the rotary drive and between the drill rods usually tend to be tightened beyond the original torque due to the considerable resistance of the subsoil to the mechanical rotation of the drill rod assembly. If both the effective drive torque and the resistance offered by the subsoil are greater than the static friction resistance between the contact surfaces of two drill rods, the threaded connection between these drill rods is tightened further. In the process, the drill rods are turned against the sliding friction resistance of their contact surfaces and are more strongly pressed together in an axial direction. 
     Given that the static friction resistance is greater than the sliding friction resistance, the torque required to unscrew the rods must be even higher than the torque with which the threaded rod connections are tightened during the drilling operation. 
     In order to have enough torque for unscrewing the drill rods with a resistive strength greater than the static friction, current systems employ a breakaway unit. In the system disclosed in EP-A-0 819820, a clamping unit is provided at the forward end of the frame, with a breakaway unit mounted immediately behind it. 
     If, for example, the drill rod assembly is to be extended by the addition of a drill rod, the first step is to stop the rotary drive in a forward retaining position on the frame. Then two hydraulically operated clamping jaws of the clamping unit are pressed against the back end of the rearward drill rod while similar clamping jaws on the breakaway unit grasp a drive chuck on the rotary drive. The clamping jaws of the breakaway unit are attached to a casing which by means of a hydraulic cylinder can be swiveled around the drill axis. For loosening the screw connection the hydraulic cylinder, turning the casing, applies a high torque on the drive chuck in a rotational direction opposite that selected for the drilling operation. This overcomes the static friction on the contact surfaces of the drive chuck and the rearmost drill rod and turns both elements by a certain angle in relation to each other. 
     The clamping jaws of the breakaway unit are then released and the rotary drive continues to turn the drive chuck with a relatively minor torque, thus completely unscrewing the threaded coupling. The rotary drive subsequently moves away from the forward direction into a rearward home position on the frame and, aided by two transport arms, inserts another drill rod. 
     The transport arms are multi-articulated gripping arms provided at their respective forward end with a hydraulically operated, more or less crescent-shaped grapple and a counter block. Actuating the hydraulic system allows the grapple to open up and, on grasping a drill rod, to close again. As the drill rod is moved between the rod magazine and the drill rod assembly, it is held between the inner surface of the grapple and the counter block. 
     A drawback of this prior-art design lies in the fact that the breakaway unit takes up much space so that an earth borer system of this type is unsuitable for drilling sites where there is not much room for accommodating the frame. Moreover, the design and operation of the transport arm in these earlier systems are rather complex and thus prone to breakdowns. 
     SUMMARY OF THE INVENTION 
     The object of this invention is a structurally uncomplicated, space-saving earth borer system incorporating a release mechanism. 
     This is accomplished for an earth borer system of the type referred to above by mounting at least one component assembly of the release mechanism on the transport arm. 
     In the earth borer system according to this invention, either the clamping unit or the breakaway unit of the release mechanism is mounted on the transport arm. This obviates the need for a separate retaining structure for the concerned components of the unit concerned on the frame of the earth borer system which latter, based on this invention, can now be built with shorter dimensions and can be deployed even under limited space conditions. 
     According to this invention, the clamping or breakaway unit mounted on the transport arm serves at least two purposes for which in conventional systems two different assemblies are needed. For one, it holds a drill rod while that rod is moved back and forth between the magazine and the drill rod assembly. For another, it permits grasping a drill rod screwed to the drill rod assembly, or the drive chuck of the rotary drive, with enough holding strength that during the breakaway, i.e. unscrewing, process it is not possible for the drill rod or, respectively, the drive chuck to turn while being clamped. If the breakaway unit is integrated into the transport arm, it serves a third purpose by providing the swivel action of this unit around the axis of the drill rod assembly. In other words, this invention combines the essentially conventional functions of multiple assemblies in one single assembly, which considerably simplifies the design of the earth borer system. 
     Another advantage of the earth borer system according to this invention is the fact that on completion of a drilling operation the drill rod assembly can be dismantled very quickly. After the respective rearward drill rod has been unscrewed, the transport arm will without further movement be in the right position for promptly returning the drill rod to the magazine. This saves the time needed after the breakaway in a conventional system for moving the transport arm to, and engaging, the rearward drill rod. 
     In a preferred and particularly simple embodiment of the earth borer according to this invention, it is the clamping unit that is attached to the transport arm. The clamping unit has fewer components than the breakaway unit and is thus especially easy to integrate in the transport arm. 
     It is equally possible, however, to mount the breakaway unit on the transport arm. Integrating the breakaway unit is more complex than attaching the clamping unit since for swiveling the unit around the axis of the drill rod assembly in traditional fashion it is necessary to provide a corresponding bearing and a drive mechanism. However, the advantage of that design variant is that even the more complex and bulky mounting structure for the breakaway unit is now no longer needed on the frame, resulting in particularly significant space savings. 
     As an especially desirable design feature, the transport arm is bearing-mounted on a pivot extending underneath the drill-rod magazine parallel to the drill axis and connected to a drive mechanism, with the clamping or breakaway unit attached to one end of the transport arm. This implementation of the transport arm requires only a simple swivel movement for transporting a drill rod back and forth between the magazine and the drill rod assembly. In other words, it is not necessary to equip the transport arm with complex articulation for which corresponding, individual drive mechanisms would be needed. A simpler design of the transport arm also makes it substantially less susceptible to technical problems. The pivoting mechanism is particularly simple, dependable and quick to operate which saves considerable time in the disassembly and reassembly of the drill rod system. 
     A transport arm, extending essentially perpendicular to the pivot axis and designed as a disk in the form of the segment of an ellipse the curved side of which points away from the pivot axis, offers an optimum in terms of stability and drive power required for swiveling the transport arm. This is due to the fact that the stated shape of the transport arm is sufficiently large in area and ruggedness to support the clamping or breakaway unit while at the same time the inertia of the transport arm relative to its pivot, and thus the amount of energy needed for the swivel motion, is relatively minor. 
     In an enhanced design version the transport arm, configured as stated, incorporates a clamping unit with two clamping jaws at least one of which is movable in relation to the other. The movable clamping jaw is preferably rotatable around a spindle on the transport arm and is powered in its swiveling motion by a hydraulic drive which as well is mounted on the transport arm. This design permits simple implementation of the action of gripping a drill rod for transfer and clamping a drill rod for unscrewing a connection. The hydraulic drive for the swivel movement of the clamping jaw can be so dimensioned as to transmit to the drill rod the necessary amount of power. Less power is needed for holding the drill rod while it is being transferred, whereas a very high power level can be selected for clamping the drill rod. 
     In another embodiment, the clamping unit is provided with elements for creating a positive, matching fit with the respective drill rods. Such positive match allows for a particularly high torque to be transferred from the breakaway unit via the drill rod to the clamping jaws without the drill rod being turned relative to the clamping jaws when a connection is unscrewed. 
     Employing interchangeable clamping inserts for the clamping jaws permits an easy conversion of the earth borer system for operation with different types of drill rods. It also permits a fairly effortless replacement of worn clamping inserts even during operation of the drilling system. 
     The clamping inserts will offer a particularly long and effective service life when made of hardened steel and provided with a rough surface finish. Surface roughness increases the static friction resistance of the clamping inserts, so that for breaking a screwed connection a higher torque can be transmitted to the drill rod. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of this invention will be evident from the description of a design example with the aid of the drawings in which - 
     FIG. 1 is a schematic overall view of the earth borer system according to this invention; 
     FIG. 2 is an enlarged lateral view of the earth borer system per FIG. 1; 
     FIG. 3 is a lateral view of a drilling ramp of the earth borer system with a drill rod magazine; 
     FIG. 4 is a frontal view of the drilling ramp with the drill rod magazine; and 
     FIG. 5 is a frontal view of a breakaway unit of the earth borer system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Shown in FIG. 1 is an earth borer system  10  according to this invention, from which a drill rod  12  with a guided drill head  14  at its tip extends into a borehole  16 . The subsoil  18  in FIG. 1 is shown in cross section to illustrate the curvature of the borehole. 
     FIG. 2 is a lateral view of a crawler-mounted earth borer system  10  whose chassis  20  is provided with a support frame  22  carrying the superstructures described below. At the forward end of the vehicle a cab  24  contains a control panel  26  and a seat  28 . Located behind the seat  26  and forming the rear wall of the cab  24  are a fuel tank  30  and a hydraulic oil tank  32 . Behind the rear wall of the cab is a diesel engine  34  with hydraulic system components. Farther back are a drilling fluid tank  36  and a mixing station  38  for the drilling fluid. 
     Attached on the far side of the earth borer system  10  and sloping toward the ground is a drilling ramp  40 , the bottom edge of its forward end resting on a support  42  which may be anchored in the ground. Connected to the top side of the drilling ramp  40  is a drill rod magazine  44 . 
     In the aft section of the earth borer system  10 , a support  46  attached to the chassis  20  can be lowered to the ground. This support  46  helps to prevent undesirable jolting of the earth borer system  10  whenever during the drilling operation the resistance of the subsoil to the advance of the drill head  14  impacts the earth borer system  10  by way of the drill rod assembly  12 . 
     FIG. 3 is a simplified lateral view of the drilling ramp  40  whose various functional elements are mounted on a frame  48 . A drive slide  50 , which can be moved back and forth along the frame  48  with the aid of a drive mechanism, not illustrated, is shown in this figure in its rearmost stop position. The back end of the drive slide has a fitting  52  for the drilling fluid. Mounted on the front end of the drive slide  50  is a rotary drive motor  54  which rotates a drill rod receptacle with a drive chuck  57 . 
     In the illustration per FIG. 3 the drill rod receptacle  56  is empty. A dotted straight line  58  indicates the position of the bore axis, that is the axis of a drill rod attached to the drive chuck  57  when the earth borer system  10  is in operation. 
     Two vertical posts  60  and  62  are mounted on the frame  48  of the drilling ramp  40  near the forward and rearward ends of the latter at approximately the same distance from an imagined, vertical central axis  64  of the drilling ramp  40 . Transport arms  66  and  68  are mounted on the support posts  60  and  62  for pivotal movement about axes  67  and  69 , respectively. Following below is a description of the transport arms with reference to FIG.  4 . 
     Mounted at the front end of the frame  48  is a breakaway unit  79 , described in more detail with reference to FIGS. 4 and 5. 
     Also mounted on the frame, as seen in FIG. 3, at approximately the same distance from the central axis  64  are a front and a rear ejector cylinder  70  and  72  which serve to push a drill rod held by the transport arms  66  and  68  back into the drill rod magazine  44  which connects to the top side of the frame  48  of the drilling ramp  40 . 
     The drill rod magazine  44  extends over essentially the length of a drill rod between the forward and the rearward end of the frame  48 . The drill rod magazine proper contains a frame  74  that is open toward the top and bottom and incorporates vertically movable retaining elements  76  which in their vertical position are paired at the front and back end of the drill rod magazine  44 . Each pair of retaining elements  76  can accept one drill rod  78 . By means of a conventional drive system, not illustrated, all retaining elements  76  can be jointly moved up and down. 
     As indicated in the simplified frontal view of the earth borer system  10  in FIG. 4, the drill rod magazine  44  contains five vertical compartments  80  to  88  for accepting the drill rods. These compartments are mutually separated by four walls  90  to  96  which are attached to upper and lower sections of the frame  74 . It is also possible to use one single drill-rod compartment which would extend in a more or less S-shaped configuration between the upper and the lower end of the drill rod magazine  44 . 
     The forward transport arm  66  is contoured roughly like a section of an ellipse with two intersecting, essentially straight sides and one curved side. The swivel axis  67  is positioned near the point of intersection of the two straight sides. To drive the swivel motion, a piston  98  of a hydraulic cylinder  100  positioned at a distance from the swivel axis bears on the transport arm  66 . Both the end of the piston contacting the transport arm and the back end of the cylinder  100  attached to the frame are swivel-mounted. This allows for a changing swivel position of the transport arm  66  as the piston  98  is extended or retracted. 
     In the swivel position of the transport arm  66  illustrated in FIG. 4, a first clamping jaw  102  integrated into the transport arm  66  and a second clamping jaw  106  which swivels around a pivot  104 , face the drill rod magazine. The pivot  104  extends perpendicular to the plane of the transport arm. The inside faces of both clamping jaws are contoured in a way that between them they can grasp and make positive contact with a drill rod. For example, they may have surface sections juxtaposed at consecutive obtuse angles as described in more detail for a clamping jaw  126  of the breakaway unit  79  (ref. FIG.  5 ). At the point where the clamping jaws  102  and  106  make contact, the surface of the drill rods or the drive chuck  57  is configured to match the shape of the jaws so that positive contact is made in the clamping process. With the aid of a hydraulic clamping cylinder  108 , the second clamping jaw  106  can be swiveled toward or away from the first clamping jaw  102 . For that purpose, the back end of the clamping cylinder  108  is swivel-mounted on the transport arm while the front end of its piston  110  is swivel-mounted on the second clamping jaw  106 . The piston  110 , positioned at a distance from the pivot  104 , bears on the second clamping jaw  106 . When a threaded coupling is to be unscrewed by operating the breakaway unit  79 , the clamping cylinder  108  can apply enough pressure to prevent any rotation of a drill rod held between the clamping jaws  102  and  106 . 
     The second transport arm  68  is similar to the first one but has no clamping unit. 
     FIG. 5 is a front view of the breakaway unit  79  mounted at the front end of the frame  48  of the drilling ramp  40 . The breakaway unit  79  incorporates a support  112  which can rotate around the axis  58  and which has two wings that extend on both sides of, and perpendicular to, an imaginary vertical central plane  114  encompassing the axis  58 . Attached to each wing of the support  112  is a clamping cylinder. As seen from the front, the forward end of the left-hand wing supports a first hydraulic clamping cylinder  116  while the rearward end of the right-hand wing supports a second, identical clamping cylinder  118 . 
     The first clamping cylinder  116  is provided with ports  120  and  122  serving as inlets and outlets for a hydraulic fluid by means of which a piston  124  can be extended in the direction of the axis  58  for clamping a drill rod or retracted so as to release the drill rod. Attached to the forward end of the piston  124  is a clamping jaw  126  whose inner surface, pointing toward the axis  58 , features juxtaposed linear sections. The center section extends at an obtuse angle of about 120° relative to the two outer sections. The two outer sections are equipped with detachable clamping inserts  128  and  130  made of hardened steel with a rough surface texture. 
     The second clamping cylinder  118  of the breakaway unit  79  is identical to the first one. 
     At the point of contact with the clamping jaws of the clamping cylinders  116  and  118 , the drill rods have a matching surface contour in the form of circumferential sections juxtaposed at an angle of about 120° relative to each other, assuring a positive grip when the drill rod is clamped. 
     The drill rod assembly  12  extends through a U-shaped opening  132  provided in the support  112  in mirror-symmetric fashion relative to the vertical center plane  114 . The open end of the U may be closed by means of a bridge  134  screwed to the top of the support. 
     For its positional retention the support  112  is provided underneath the opening  132  with a routed slot  136  which in circular fashion extends around a center point on the axis  58  and is likewise mirror-symmetrical relative to the vertical center plane  114 . Two pillow block bolts  140  and  142 , mounted in a pedestal  138  that connects to the frame  48 , extend through the slot  136  parallel to the axis  58  and hold the support  112  even when it swivels around the axis  58  of the drill rod assembly. 
     The rotation of the breakaway unit  79  is driven by a breakaway cylinder  144  whose piston  146  bears on the right wing of the support  112  to the side of the axis  58 . For that purpose the forward end of the piston  146  is swivel-mounted on the support  112  by way of an articulated joint  148 . A cantilever  150  screwed to the pedestal  138  holds the cylinder  144  on an articulated joint  152 . By virtue of this arrangement the breakaway cylinder  144  cannot rotate under the pressure axially exerted on the piston  146  when the support  112  is pivoted. 
     To separate a screwed connection between the drive chuck  57  and a drill rod, the clamping jaws  102  and  106  of the clamping unit of the transport arm  66  grasp the drive chuck  57  and the clamping jaws  126  of the breakaway unit  79  grasp the drill rod. The breakaway cylinder  144  is then actuated and the drill rod is swiveled with the breakaway unit  79  by about 40° against the drilling direction of rotation of the drill rod, while the drive chuck  57  is held stationary.

Summary:
This invention relates to an earth borer system with a frame ( 48 ) incorporating a moveable rotary drive ( 50, 54 ) for a drill rod assembly consisting of at least two drill rods which can be detachably connected with one another along a bore axis ( 58 ); with a drill rod magazine ( 44 ) attached to the frame ( 48 ); with a release mechanism positioned on the frame provided with a clamping unit ( 102, 104, 106, 108, 110 ) that engages in a first drill rod and a breakaway unit that engages in one section of the rotary drive ( 50, 54 ) or in a second drill rod; and with at least one transport arm ( 66 ) that is attached to the frame and which can move a drill rod released from the drill rod assembly into a standby position in the drill rod magazine ( 44 ) or retrieve a drill rod from its standby position and place it on the drill rod assembly. According to this invention, at least one component unit of the release mechanism is mounted on the transport arm ( 66 ).