Patent Publication Number: US-11661797-B2

Title: Mining or construction vehicle and a hydraulic cylinder conduit enclosing a conduit arrangement

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage application of PCT/EP2018/065311, filed Jun. 11, 2018 and published on Mar. 14, 2019 as WO/2019/048094, which claims the benefit of Swedish Patent Application No. 1751090-0, filed Sep. 8, 2017, all of which are hereby incorporated by reference in their entireties. 
     TECHNICAL FIELD 
     The invention relates to a mining or construction vehicle and to a hydraulic cylinder enclosing a conduit arrangement in connection to a mining or construction vehicle. Specifically, the invention involves a conduit arrangement adapted to be extended during operation. 
     BACKGROUND 
     In mining and construction industry hydraulic devices, such as a rock drilling machines, are often arranged on a movable arm or the like of a mining or construction vehicle. Such hydraulic devices often include several hydraulic components which need to be supplied with hydraulic fluid, and in some cases flushing medium and pressurised air also need to be supplied to the hydraulic device, such that additional conduits need to be provided along the movable arm. 
     In WO 2006/096110 A1 a rotation device for a boom of a mining or construction work rig is disclosed. The arrangement of WO 2006/096110 A1 comprises a hydraulic device in the form of a drilling machine. Although not shown in the disclosure of WO 2006/096110 A1, the hydraulic device therein is provided with hydraulic fluid via hoses arranged in flexible reel arrangements allowing the different parts of the rig arm arrangement to rotate and pivot with respect to each other. 
     Such a system is problematic due to the fact that the hoses are exposed to the harsh environment of a mining or construction vehicle risking that a hose may rupture. Conventionally, a major part of the downtime of a mining or construction vehicle with a hydraulic device arranged on an arm that extends out from the vehicle is due to problems with the provision of hydraulic fluid in one way or another. Further, the many hoses may impede the visibility for the operator controlling the mining or construction vehicle. 
     Hence there is a need of an arrangement that improves the conduit arrangement on a mining or construction vehicle. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a mining or construction vehicle with an improved conduit arrangement. 
     According to a first aspect the invention relates to mining or construction vehicle with an extendable boom comprising at least a first and a second telescopic section extending in a longitudinal direction, wherein the first telescopic section is arranged to be connected to the mining or construction vehicle and a hydraulic device is arranged to be connected to a mounting device in connection to a free end of the second telescopic section, wherein a hydraulic cylinder is arranged in connection to the extendable boom to govern extension of said extendable boom. Further, a at least one hydraulic conduit for supply of hydraulic fluid to the hydraulic device on the mounting device is arranged inside the extendable boom. 
     In a specific embodiment, the hydraulic cylinder is arranged inside the extendable boom. Further, the hydraulic conduit for supply of hydraulic fluid to the hydraulic device may be arranged inside said hydraulic cylinder. 
     In a specific embodiment, the hydraulic conduits are arranged through the free end of the second telescopic section of the extendable boom. Preferably, the hydraulic conduit extends substantially in parallel with the extendable boom in the longitudinal direction out from the free end of the second telescopic section of the extendable boom. The conduit for supply to the hydraulic device may be telescopically extendable. 
     In a specific embodiment, the mining or construction vehicle is a drill rig and the hydraulic device is a hydraulic percussive drilling machine. 
     Further, the hydraulic percussive drilling machine comprises a percussive unit and wherein the hydraulic conduit is arranged to supply the percussive unit with hydraulic fluid. 
     In a specific embodiment, the four different hydraulic conduits are arranged alongside inside the extendable boom, a first conduit to a percussive unit of the drilling machine, a second conduit to a rotation motor of the drilling machine, a third conduit to a feed device for feeding the drilling machine back and forth, and a fourth conduit for a return flow to tank. 
     According to a second aspect the invention relates to a hydraulic cylinder, in which hydraulic conduits are arranged for feeding pressurised hydraulic fluid to a hydraulic device, wherein a command unit is arranged to command the extension of the hydraulic cylinder, a sensor is arranged to monitor the extension of the hydraulic cylinder, and a control unit is arranged to compare said monitored extension with the commanded extension. 
     In a specific embodiment, an alert signal is issued when the control unit detects a discrepancy between the monitored extension and the commanded extension of the hydraulic cylinder. 
     In one specific embodiment, a feed system is arranged to compensate a fluid volume in at least one conduit for supply of hydraulic fluid to the hydraulic device, and wherein the control unit is arranged to control a supply of hydraulic fluid to the hydraulic conduit corresponding to the increased volume of said hydraulic conduit, and, when the hydraulic conduit is compacted, the control unit is arranged to control a discharge of hydraulic fluid from the hydraulic conduit corresponding to the decreased volume of said hydraulic conduit due to that it is being compacted. 
     In one specific embodiment, the hydraulic device is a rock drilling machine that may operate at a different hammering frequencies, and wherein the control unit is arranged to control the operation of the drilling machine so as to avoid hammering frequencies that has been identified to be prone to produce resonances in the hydraulic conduit and/or to control the extension of the extendable boom so as to avoid an extension of the hydraulic conduit that may interfere with a desired hammering frequency. 
     The invention also relates to a mining or construction vehicle comprising an extendable boom with at least a first and a second telescopic section extending in a longitudinal direction, wherein the first telescopic section is arranged to be connected to the mining or construction vehicle and a hydraulic device is arranged to be connected to a mounting device in connection to a free end of the second telescopic section, which mining or construction vehicle comprises a hydraulic cylinder as described above, in which at least one hydraulic conduit is arranged for feeding pressurised hydraulic fluid to the hydraulic device. 
     In another embodiment, the invention may relate to an extendable boom comprising at least a first and a second telescopic section extending in a longitudinal direction, wherein a hydraulic percussive drilling machine is arranged to be connected to a mounting device in connection to a free end of the second telescopic section, wherein a cylinder is arranged in connection to the extendable boom, and wherein at least one hydraulic conduit, typically a telescopic conduit, for supply of hydraulic fluid to the hydraulic device on the mounting device, is arranged inside the hydraulic cylinder, at least partly embedded in a fluid, e.g. a hydraulic fluid, inside said hydraulic cylinder. 
     The cylinder comprising the at least on hydraulic conduit may be a hydraulic cylinder arranged to also govern the extension of the extendable boom or, as an alternative, the extension may be governed by a second hydraulic cylinder. 
     By arranging the at least one hydraulic conduit inside the hydraulic cylinder, at least partly embedded in a hydraulic fluid, the self-oscillation of said hydraulic conduit will be restricted. This is useful both if the hydraulic cylinder is arranged inside the extendable boom or on the outside of the extendable boom. The fluid may be the hydraulic fluid arranged as working fluid inside the cylinder, but it can also be another fluid specifically chosen to dampen oscillations of the conduits. 
     Other embodiments and advantages of the invention will be apparent from the, dependent claims, detailed description and the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       An exemplary embodiment related to the invention will now be described with reference to the appended drawings, in which; 
         FIG.  1    is a schematic view of a mining or construction vehicle, 
         FIG.  2    is a schematic view of an extendable boom, 
         FIG.  3    is an illustrative view of the geometry of the free end of an extendable boom, 
         FIG.  4    is an illustrative view of a conduit arrangement at the free end of an extendable boom, 
         FIG.  5    is a view of hydraulic cylinder with an internal conduit arrangement, 
         FIG.  6    is a longitudinal cut view of the hydraulic cylinder in  FIG.  5   , 
         FIG.  7    is a perspective view of the piston part of a hydraulic cylinder, 
         FIG.  8    is a schematic view of a boom with an alternative angle unit, 
         FIG.  9    is a sectional view of the alternative angle unit of  FIG.  8   , and 
         FIG.  10    is a perspective view of the alternative angle unit of  FIG.  8   . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In  FIG.  1    a mining or construction vehicle  10  according to an aspect of the invention is shown. The mining or construction vehicle  10  comprises an extendable boom  12  with a first and a second telescopic section  13  and  14 , respectively, extending in a longitudinal direction D 1 , i.e. the axial direction, of the extendable boom  12 . The first telescopic section  13  is arranged to be connected to the mining or construction vehicle  10  and a hydraulic device (not shown) is arranged on a mounting device  11  in connection to a free end  18  of the second telescopic section  14  of the extendable boom  12 . In a specific embodiment, the vehicle is a drill rig and the hydraulic device is a hydraulic rock drilling machine, typically comprising a percussive drill hammer. The mounting device  11  of the shown embodiment is arranged in connection to the free end  18  of the second telescopic section  14 , but the fact that it is arranged in connection to a free end  18  of the second telescopic section  14  of the extendable boom  12  should be construed as it may be arranged at a distance from the extendable boom  12 , e.g. connected via a further boom or the like. 
     The extendable boom  12  may comprise more than two telescopic sections, wherein additional sections may be telescopically arranged between the first and second telescopic sections  13  and  14 . In the shown embodiment, the mounting device  11  arranged to carry the hydraulic device is arranged on a pivot arm at the free end  18  of the extendable boom  12 . The mounting device  11  may e.g. be comprised of a mounting plate, a bracket, a holder or a set of mounting holes for attachment of a hydraulic device. 
     The extendable boom  12  is shown in a longitudinal section in  FIG.  2   . A hydraulic cylinder  19  is arranged in connection to the extendable boom  12  to govern the extension of said extendable boom  12 . In the shown embodiment, the hydraulic cylinder  19  is arranged inside the extendable boom  12 . The extendable boom  12  is connected to the hydraulic device arranged on the mounting device  11  via a first and a second rotation device  15  and  16 , respectively. 
     As is illustrated in  FIG.  3   , the first rotation device  15  is arranged at a free end  18  of the extendable boom  12  to provide a rotation R 1  around a first axis A 1  that is substantially parallel to the longitudinal direction D 1 . In the shown embodiment, the first axis A 1  coincides with and is parallel to the longitudinal direction D 1  of the extendable boom  12 . The second rotation device  16  is arranged to provide a rotation R 2  around a second axis A 2  that is arranged at an angle with respect to the first axis A 1 . The rotation devices are interconnected by an angle unit  32 , which comprises an intermediate part  37  with a first attachment device for attachment to a rotating part of the first rotation device  15 , and a second attachment device for attachment to the second rotation device  16 . The first and second attachment devices of the intermediate part  37  are arranged at an angle with respect to each other, said angle corresponding to the angle between the first rotation axis A 1  and the second rotation axis A 2 . This angle is preferably about 90° and preferably larger than 60° or more preferably larger than 80°, and preferably smaller than 120°, more preferably smaller than 110°. 
     The hydraulic device arranged on the mounting device  11  needs pressurised hydraulic fluid to function. The pressurised hydraulic fluid is provided from a pressure source  30  on the mining or construction vehicle  10 . In the shown embodiment, the hydraulic conduits  17  for supply of hydraulic fluid to the hydraulic device are arranged through the extendable boom  12 . Specifically, the hydraulic conduits  17  are arranged inside the hydraulic cylinder  19 . Further, additional conduits, such as conduits for providing flushing medium and pressurised air to the hydraulic device are provided. In a preferred embodiment, such additional conduits are also arranged inside the extendable boom  12 . 
     In a not shown embodiment the hydraulic cylinder  19  may be arranged outside of the extendable boom  12 . The hydraulic conduits  17  may however still be arranged inside the extendable boom  12 . Further, both the hydraulic cylinder  19  and the hydraulic conduits  17  may be arranged inside the extendable boom  12 , side by side, i.e. with the hydraulic conduits inside the extendable boom  12  but outside the hydraulic cylinder  19 . 
     In the embodiment shown in  FIG.  4   , the hydraulic conduits  17 , which are arranged for supply of hydraulic fluid to the hydraulic device arranged on the mounting device  11 , extend through both the first and second rotation devices  15  and  16 . 
     In another not shown embodiments the hydraulic conduits  17  are arranged through only one of the rotation devices, either the first or second rotation device  15  or  16 . In such a case, the hydraulic conduits  17  are arranged past the other rotation device on the outside of it. 
     In the shown embodiment, the hydraulic conduits  17  are arranged through the free end  18  of the extendable boom  12 , i.e. through the free end of the second telescopic section  14 . The hydraulic conduits  17  extend substantially in parallel with the extendable boom  12  in the longitudinal direction D 1  out from the free end  18  of the extendable boom  12 . Specifically, the hydraulic conduits  17  are arranged to extend through an end part of the hydraulic cylinder  19  and further out through the free end  18  of the extendable boom  12 . In the shown embodiment, the conduits  17  for supply to the hydraulic device are telescopically extendable, which will be more closely described below. 
     The first rotation device  15  is arranged at a free end  18  of the extendable boom  12 , wherein the first rotation device  15  has a through hole and wherein the hydraulic conduits  17  are arranged through said through hole of the first rotation device  15 . Further, in the shown embodiment, the second rotation device  16  also comprises a through hole, wherein the hydraulic conduits  17  are arranged through said through hole of the second rotation device  16 . In a specific embodiment the rotation devices are hydraulically driven worm gear motors with an external drive allowing the hydraulic conduits  17  to pass through the centre of the first or second rotation device, or both. A skilled person will know that are other ways of providing a rotational motor with a central through hole allowing conduits to pass centrally, an example being a hydraulic motor with a centrally located swivel arrangement. 
     In order to allow the conduits to rotate with the rotation of the rotation devices a swivel arrangement  20  is arranged. In the shown embodiment, each conduit is swiveled twice, on both sides of an angle of about 90°. A first set of swivels  23  are arranged to allow the conduits extending through the first rotation device to rotate around an axis that is substantially parallel to the first axis or rotation A 1  of the first rotation device  15 . A second set of swivels  24  are arranged to allow the conduits  17  to rotate around an axis that is substantially parallel to the second axis of rotation A 2  of the second rotation device  16 . Each swivel may e.g. be a rotatable hose coupling. Instead of sets of individual swivels the swivel arrangement may comprise one or two multi-swivels providing a swivel connection for a plurality of hydraulic conduits. 
     Further, in a not shown embodiment such a multi-swivel may be a part of a rotation device  15  or  16 , and provided centrally inside said rotation device. In such a multi-swivel the conduits may be connected axially to the multi-swivel of the first rotation device  15  from the inside of the extendable boom  12 . The swiveled conduits may extend either axially or radially out from the free end of the extendable boom. A similar arrangement may be arranged at the second rotation device  16 , with conduits arriving either radially or axially with respect to the second axis of rotation A 2  from the first rotation device. The swiveled fluid conduits preferably extend axially out from the second rotation device  16  towards the hydraulic device arranged on the mounting device  11 . If the conduits are arranged radially from the first rotation device  15 , they will extend axially out from the second rotation device  16 , whereas they may extend either radially or axially to the hydraulic device if the conduits enter axially from the first rotation device  15 . 
     Between the sets of swivels  23  and  24  or multi-swivels, hydraulic connectors  27 , e.g. individual connectors, are provided, which hydraulic connectors in conjunction with the set of swivels  23  and  24  form an angle that correspond to the angle between the first and second axis of rotation A 1  and A 2 , respectively. In the shown embodiment, this angle is about 90°. The angle is preferably larger than 60° or more preferably larger than 80°, and smaller than 120°, more preferably smaller than 110° or even 100°. In one specific embodiment only one set of swivels, or one multi-swivel is arranged for any which one of the rotation devices, wherein the conduits are arranged to flex along with the rotation of the other rotation device. 
     A valve unit  25  is arranged at the mounting device  11 , or in connection to the second rotation device  16 . The valve unit  25  is arranged to provide the different functions of the hydraulic device with a hydraulic pressure. The valve unit  25  allows the number of conduits that need to be arranged to the hydraulic device to be minimised. At least one of the hydraulic conduits  17  is a pressure line from a pressure source arranged on the mining or construction vehicle. In addition to the at least one pressure line a return line leading to tank needs to be arranged. In a specific not shown embodiment, these are the only two hydraulic conduits that are arranged along, and preferably inside, the extendable boom  12 . 
     A diverter valve  26 , separate from the valve unit  25 , may be arranged to provide the rotation motors  15  and  16  with pressurised hydraulic fluid. 
     In a specific embodiment, the hydraulic device is a rock drilling machine. A rock drilling machine normally needs three hydraulic pressurised inputs, a first input for the percussion of the drill string, a second input for the rotation of the drill string and a third input for the forward feed of the drilling machine in the drilling direction. In one embodiment, these three inputs may be provided from one combined hydraulic supply conduit. However, in many applications it may be advantageous to provide these different functions with separate supply lines, because the pressure and flow may vary greatly between different functions such that they may influence each other. 
       FIG.  5    shows a partly cut view of an exemplary embodiment of hydraulic conduits  17 A-D arranged inside a hydraulic cylinder  19  that is arranged to govern the extension of the extendable boom  12 . In this embodiment, the hydraulic conduits  17  are comprised of four different conduits, a first conduit  17 A to a percussive unit of the drilling machine, a second conduit  17 B to a rotation motor of the drilling machine, a third conduit  17 C to a feed device for feeding the drilling machine back and forth, and a fourth conduit  17 D for a return flow to tank. 
     These are exemplary uses for the different conduits and it is obvious to a person skilled in the art that more conduits may be arranged, or less, and that other applications in need of a hydraulic supply may be used. Also shown in  FIG.  5    are the hydraulic connections  34  and  35  providing the hydraulic cylinder  19  with hydraulic fluid, and a conduit  33  to the rod side of the hydraulic cylinder  19 . 
       FIG.  6    is a cut view along the longitudinal direction D 1  of the hydraulic cylinder  19 . From this view it is apparent that that each hydraulic conduit  17 A-D is telescopic, comprising two tubular sections each, whereof a smaller tubular section is arranged to slide within a relatively larger tubular section. The individual hydraulic conduits may also comprise three or more telescopic sections. Specifically, the embodiment with three telescopic sections may be made neutral with respect to pressure and volume, such that a conduit may expand lengthwise without affecting its interior volume or the pressure inside it. As is apparent from  FIG.  6    the hydraulic conduits  17  extend through the piston end part  36 , substantially parallel with the longitudinal direction D 1  of the extendable boom  12 . 
     In  FIG.  7    it is shown how the hydraulic conduits  17  extend through the piston end part  36  from where they will continue through the free end of the extendable boom  12 . 
     A sensor  21  is arranged to monitor the extension of the extendable boom  12  in the longitudinal direction D 1 . The sensor  21  may be arranged on anyone of the moving parts, i.e. on the extendable boom  12  or on the hydraulic cylinder  19 . A control unit  22  is arranged to control operation of the hydraulic device and to monitor other operations of the mining or construction vehicle  10 , see  FIG.  1   . The control unit  22  is inter alia arranged to monitor commands issued by an operator, such as commands relating to the extension of the extendable boom  12  in the longitudinal direction D 1 . The control unit  22  may physically be arranged anywhere, e.g. on the mining or construction vehicle  10 , on the extendable boom  12 , or at a distant location in communication with a communication unit at the mining or construction vehicle  10 . 
     The control unit  22  is also arranged to compare the commanded extension of the extendable boom  12  with the actual extension as monitored by the sensor  21 . Such a comparison may be made as a method of detecting a leak in anyone of the hydraulic conduits arranged inside the hydraulic cylinder  19 . If the actual extension as monitored by the sensor  21  is greater than the commanded extension of the extendable boom  12  this may be due to a leak in one of the pressurised hydraulic conduits  17 A-C. Namely, the leaking pressurised hydraulic fluid from the pressurised hydraulic conduits  17 A-C will leak into the hydraulic cylinder, mixing with the hydraulic fluid of the hydraulic cylinder and causing the piston of the hydraulic cylinder to extend so as to extend the extendable boom  12 . Alternatively, if a low-pressure conduit, such as the return conduit  17 D, is broken fluid may leak from the hydraulic cylinder and into said return conduit  17 D such that an undesired retraction of the extendable boom may be noted. 
     If such undesired extension or retraction is noted, i.e. if the monitored extension does not correspond to the commanded extension, an alert signal may be issued, or under certain conditions the system may be shut down and/or the operation interrupted. The operation may be resumed only after the problem has been identified and attended to. The distinction between issuing a warning signal and system shut down may be decided by the magnitude of the discrepancy, such that when a discrepancy exceeding a first threshold is noted a warning signal is issued, and when a discrepancy exceeding a second threshold, which is greater than the first threshold, is noted the system is shut down and/or the operation interrupted. In a specific embodiment, the control unit  22  may be arranged to govern a compensation of the discrepancy, e.g. by providing excess hydraulic fluid to a hydraulic cylinder from which hydraulic fluid is lost into a low-pressure conduit, or to allow hydraulic fluid to escape from a hydraulic cylinder into which hydraulic fluid leak from a high-pressure conduit. Such compensation is hence governed by means of the control unit to make sure that a small leak is compensated for. If it becomes apparent that such compensation is not successful or does not meet a desired level of accuracy, e.g. if a discrepancy exceeding a specific threshold is noted, the operation may be aborted. 
     The arrangement of detecting leaks inside a hydraulic cylinder may be used irrespective of where the hydraulic cylinder is arranged. It is however specifically useful in applications where a hydraulic device is arranged on an extendable boom such that hydraulic conduits will need to be arranged along or inside the extendable boom. 
     The control unit  22  may also be arranged to control the operation of the hydraulic device in dependence of the extension of the extendable boom  12 . Typically, a hydraulic device includes a hydraulic motor that works in a specific frequency. In the example where the hydraulic device is a drilling machine it comprises a percussion hammer producing strong hydraulic pulses by means of which a drill string is intermittently pushed further into the material being drilled to form a bore hole into/through the same. These pulses are produced with a specific frequency, which is adaptable as one of several drilling parameters in order to optimize a drilling operation. Conventionally, the frequency may e.g. be adapted as a function of the properties of the material in which the drilling is performed. 
     A problem that needs to be considered with extendable hydraulic conduits  17  is the vibration of the hydraulic device, which may cause resonance problems in the hydraulic conduits. Resonance may lead to detrimental vibrations causing instability, fatigue and, as a worst case, total break-down of the system. Each conduit may be regarded as a trombone pipe with a specific resonance frequency, which is a direct function of the length of said hydraulic conduit. If this resonance frequency coincides with a frequency of a vibrating or oscillating hydraulic device, such as a rotating drilling machine or a percussion hammer, the conduit may start to self-oscillate, thereby risking serious negative consequences. Especially, the frequency of a percussive hammer of a hydraulic percussion rock drill needs to be considered. The percussions of the percussive creates pulsations that may propagate backwards through the hydraulic medium in the first conduit  17 A to a percussive unit of the drilling machine. During a continuous drilling operation, these pulsations will have a frequency corresponding to the frequency of the percussive hammer. 
     Therefore, the control unit  22  may be arranged to operate a hydraulic device such as a percussive drilling machine so as to avoid operating frequencies that has been identified to be prone to produce resonances and/or self-oscillation. Hence, drilling frequencies that may be prone to produce resonances are identified for specific extensions of the extendable boom  12 . Subsequently, during a drilling operation, the control unit  22  is arranged to compare a current extension of the extendable boom  12  with a current drilling frequency of the drilling machine. If it is noted that a commanded drilling frequency may be prone to produce a resonance at the current extension of the extendable boom  12 , the control unit will issue a warning or a command to avoid said commanded drilling frequency. The drilling machine may then be set to operate at a different drilling frequency that has not been identified as prone to produce a resonance at the current extension of the extendable boom  12 , or the extension of the extendable boom  12  may be altered. 
     However, often during a drilling operation, it is desired not to move the mining or construction vehicle  10  or to adjust its position or settings, e.g. by changing the extension of the extendable boom  12 . However, in most operation the frequency range that will be used for a specific operation will be known before start of the operation. Therefore, the set-up of the drilling or construction vehicle preferably set up so as to avoid an extension of the extendable boom corresponding to a length of a hydraulic conduit that may risk to interfere with the drilling frequency range to be used. Namely, often it is possible to locate a hydraulic device arranged in connection to an extendable boom, and specifically, a drilling end of a drilling machine at one specific location by adapting other parameters than the extension of the extendable boom, such as e.g. the position of the drilling or construction vehicle, the angles of the extendable boom with respect to both the vehicle and/or the feed beam. 
     Therefore, in order to avoid resonance in a hydraulic conduit during an ongoing drilling operation, it is possible to adjust the drilling frequency, but for most applications it desirable to adapt the position of the vehicle, e.g. drill rig, beforehand so as to make sure that the desired drilling frequencies may be used without causing problems. 
     In a specific embodiment, an attenuator may be arranged to attenuate the vibration of the hydraulic conduits. The fact that the hydraulic conduits  17  are arranged inside the hydraulic cylinder  19 , embedded in a hydraulic fluid, will dampen their possibilities to oscillate and hence also restrict the self-oscillation of the hydraulic conduits  17 . This is particularly useful for the conduit  17 A to the percussive unit of the drilling machine, and in one embodiment only the conduit  17 A to the percussive unit of the drilling machine is embedded inside the hydraulic cylinder  19 . Nevertheless, it may still be of importance to dampen the possibility of self-oscillation of the hydraulic conduits  17  by avoiding specific drilling frequencies in combination with specific extensions of the extendable boom  12 . 
     A hydraulic feed system  31  comprising a supply tank and a pump may be arranged in connection to the hydraulic cylinder  19  to compensate a fluid volume in at least one of the hydraulic conduits  17  for supply to a drilling machine. When the extendable boom  12  is extended, the volume inside the hydraulic conduits  17  is increased. The control unit  22  may be part of the hydraulic feed system and is arranged to control a compensation by supplying a hydraulic flow to the hydraulic conduit corresponding to the increased volume of said hydraulic conduit. Correspondingly, when the extendable boom  12  is compacted, the control unit  22  may be configured to control a compensation by allowing a hydraulic flow corresponding to the decreased volume of said hydraulic conduit to escape from the hydraulic conduit. In order to avoid cavitation and a negative pressure in the hydraulic conduits a consumer may be connected to the return line to make sure that too much hydraulic fluid is not drawn from the conduits. 
     In  FIGS.  8 - 10    an alternative angle unit  32  is shown. This angle unit  32  is arranged on a boom  12  extending in a first direction D 1 . The boom  12  is connected to a mining or construction device arranged on a mounting device  11 , via a first and a second rotation device  15 , and  16 , arranged in connection to the free end of said boom  12 . The mining or construction device is preferably a device for producing holes in a rock or the like, e.g. a rock drilling device. In a specific embodiment it is a hydraulic rock drilling machine. 
     Preferably the mining or construction device is a drill rig including a rock drilling machine arranged on a mounting device  11 . 
     Preferably the boom  12  is extendable, comprising a first telescopic section  13  and second telescopic section  14 . 
     The first rotation device  15  is arranged to provide a rotation around a first axis A 1  that is substantially parallel to the first direction D 1 , and the second rotation device  16  is arranged to provide a rotation around a second axis A 2  that is arranged at an angle with respect to the first axis A 1 . In an alternative embodiment, the first rotation device  15  is arranged inside the boom, specifically an extendable boom. In such an arrangement the second telescopic section  14  is cylindrical and arranged with splines inside the first telescopic section  13 . The first rotation device may be arranged inside the first telescopic section  13  to be translated along with the inner end of the second telescopic section  14 . Such an arrangement is described in detail in EP 0 434 652 and may be implemented on the inventive mining or construction vehicle. 
     The angle unit of this embodiment is different with respect to the embodiment shown in  FIGS.  1 - 4   . Namely, in contrast to the embodiment shown in  FIGS.  1 - 4    a pivot point  40  is arranged between said first and second rotation devices  15  and  16  to provide an angular movement of said second axis A 2  of said second rotation device  16  with respect to said first axis A 1  of said first rotation device  15 . Conventionally, such a pivot point  40 , if at all present, is arranged outside of both the rotation devices  15  and  16 . The angular movement may be used to alter the tilt angle of a feed beam, not show, including a drilling machine arranged on the mounting device  11  into suitable drilling angles. Except from this difference the arrangements of the different embodiments of the angle unit  32  may be combined in any possible way. 
     As noted above, the angle unit  32  of the embodiment shown in  FIGS.  8 - 10    comprises a pivot point  40  arranged between said first and second rotation devices  15 , 16  and a pressure cylinder  39  arranged to provide the angular movement of the second axis A 2  of the second rotation device  16  with respect to the first axis A 1  of said first rotation device  15  around said pivot point  40 . In the shown embodiment, the first rotation device  15  is arranged at the outer end of second telescopic section  14  of an extendable boom  12 . Thereby, space is limited for the arrangement of the angle unit  32 . 
     In view of the limited space between the first and second rotation devices  15 , 16  a first arm  41  extends backwards with respect to the direction D 1  of the boom  12 , so as to prolong the working length of the pressure cylinder  39  and make it possible to have a shorter angle unit  32  between the rotational units  15 ,  16 . Specifically, the first arm  41  is arranged to extend backwards with respect to the first direction D 1  of the boom  12  from a point at an outer end of said boom  12  so as to rotate with said rotation device  15 , said first arm  41  being connected at a first end of the pressure cylinder  39 . The opposite, second end of the pressure cylinder  39  is connected to a second arm  42  arranged at the second rotation device  16 . The arms  41  and  42  may be a narrow arm structure as shown in  FIGS.  8 - 10    or a structure partly or fully enclosing the rotational devices  15 ,  16 . 
     The angle unit  32  shown in  FIG.  8 - 10    comprises a first part  32   a  connected to the first rotation device  15  and a second part  32   b  connected to the second rotation device  16  wherein the first and second parts of the angle unit  32  are connected to each other in the pivot point  40 . The first arm  41 , which extends backwards with respect to the direction D 1  of the boom  12  and rotates with the rotation device  15 , extends past the connection between the first part and the first rotation device  15 . The second arm  42  is connected to the second part and extends along the second axis A 2  past the connection between the second part and the second rotation device  16 . The arms  41  and  42  may be made integral, welded or bolted to the first and second parts of the angular unit  32 . An alternative design, not shown, would be to make the first and/or second parts of the angle unit  32  longer to include the connection points for the pressure cylinder  39 . However this will increase the length along the axis A 1  and/or A 2  and size of the angle unit in a non-desired way. The angle unit  32  is preferably bolted to the first and second rotational device  15 ,  16  for easy connection and disconnection. 
     In the shown embodiment second arm  42  extends past at least a part of the second rotation device  16  along the second axis A 2 . The main object of the second arm  42  in this embodiment is not to increase the pivot length with respect to the pivot point  40 , but to allow a compact and reliable arrangement. Therefore, the second arm  42  extend along the second axis A 2  past at least a part of the second rotation device  16 , thereby allowing the pressure cylinder  39  to be arranged inside the angle between the first and second axis A 1  and A 2 . Thereby, an extension of the pressure cylinder  39  will act to increase the angle between the first axis A 1  and the second axis A 2  and a retraction of the pressure cylinder  39  will act to decrease said angle. 
     In an alternative, not shown embodiment, one or two pressure cylinders may be arranged at the outer end of the angle arrangement, i.e. on the outside of the angle, such that a extension of the pressure cylinder  39  will act to decrease the angle between the first axis A 1  and the second axis A 2  whereas a retraction of the pressure cylinder  39  will act to increase said angle. In this alternative the second arm  42  will extend in the opposite way, along the second axis A 2 , away from the second rotation device  16 . In this way, the outer end of the second arm will become visible below the boom  12 . 
     In the shown embodiment the first part  32   a  of the angle unit comprises a first hinge limb pair  43  that extends from the first rotation device  15  and is connected at the pivot point  40  to a second hinge limb pair  44  of the second part  32   b  of the angle unit. As is visible in  FIG.  10   , the hydraulic connectors  27  are arranged to pass between the first hinge limb pair  43 , inside the pivot point  40  and between the second hinge limb pair  44 . Hence, in this embodiment, the pivot point is comprised of two spaced apart hinges, connecting the first and second hinge limb pairs  43  and  44  to each other and providing a space in between allowing e.g. the hydraulic conduits  27  to pass inside said spaced apart hinges. 
     In the embodiment shown in  FIGS.  9  and  10    the first rotation device  15  comprises a first swivel arrangement  23  and the second rotation device  16  comprises a second swivel arrangement  24  for supply of hydraulic fluid to the hydraulic device on the mounting device  11 . Hydraulic connectors  27 , typically in the form of flexible conduits, are arranged to connect the first swivel arrangement  23  to the second swivel arrangement  24 . 
     Also, in the shown embodiment, a valve unit  25  for the distribution of hydraulic fluid to and from the hydraulic device is arranged in direct connection to the second swivel arrangement  24 . They may eve be arranged as one integral unit. The close connection between the valve unit  25  and the second swivel arrangement  24  is advantageous as it saves place and it is made possible in that the pivot point is arranged between the first and second rotation devices  15  and  16 . Namely, with such an arrangement, the hydraulic conduits downstream of the second rotation device  16  need only be compensated for the translational movement of the hydraulic device along the feed beam  11 , which is predictable and easily compensated for. The hydraulic connectors  27  arranged between the swivels  23  and  24  are configured to cope with the angular movement of the angle unit  32 . In a similar way, the hydraulic conduits  17  through the piston end part  36  may be directly connected to the first swivel arrangement  23 . 
     In the shown embodiment the hydraulic fluid to and from the hydraulic device is arranged through the first and second swivels  23  and  24  arranged in connection to the first and second rotation devices  15  and  16 , respectively. The swivels  23  and  24  may be fully or partly located in opening through the rotation devices  15  and  16 . In an alternative, not shown embodiment, the hydraulic conduits may be arranged in a more conventional manner outside of the boom  12  and/or the angle unit  32 . The use of a pivot point arranged between the first and second rotation devices  15  and  16  is hence not dependent of that the hydraulic conduits are internally drawn. For an arrangement where the hydraulic conduits are drawn around the angle unit  32  other types of motors, which do not include a hole through their centres, may be utilised. 
     Above, the invention has been described with reference to specific embodiments. The invention is however not limited to these embodiments. It is obvious to a person skilled in the art that other embodiments are possible within the scope of the following claims. The terms “comprising” and “comprised of” is used in this application in a non-exclusive meaning, such that all comprised parts may be completed with additional parts.