EP2328723A1

EP2328723A1 - Method and arrangement in rock drilling rig

Info

Publication number: EP2328723A1
Application number: EP09817334A
Authority: EP
Inventors: Markku Keskiniva; Juha Piispanen; Mauri Esko; Aimo Helin
Original assignee: Sandvik Mining and Construction Oy
Current assignee: Sandvik Mining and Construction Oy
Priority date: 2008-09-30
Filing date: 2009-09-30
Publication date: 2011-06-08
Anticipated expiration: 2029-09-30
Also published as: CN102164714A; WO2010037905A1; JP5399498B2; FI20085926A7; CL2011000680A1; CN102164714B; JP2012504197A; FI122300B; CA2735772A1; FI20085926A0; AU2009299713A1; AU2009299713B2; EP2328723B1; CA2735772C; ZA201101642B; EP2328723A4

Abstract

A rock drilling rig (1) is provided with a rock drilling machine (6) comprising an impact device (4), a feed device (9) and a tool (7) with a drill bit (8) at the end thereof for breaking rock. The impact device is arranged to cause a stress wave to the tool and from there further to the rock to be drilled. During drilling at least some of the compressive stress wave (σ_i) caused to the tool is reflected as a stress wave (σ_r) from the rock back to the tool. The method comprises determining a momentum ( P_r ) of the stress wave ( σ_r) reflected from the rock to the tool and adjusting the operation of the impact device and/or that of the feed device on the basis of the momentum.

Description

METHOD AND ARRANGEMENT IN ROCK DRILLING RIG

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method for controlling a rock drilling rig, the rock drilling rig being provided with a rock drilling machine comprising an impact device, a feed device and a tool with a drill bit at the end thereof for breaking rock, and the impact device being arranged to cause a stress wave to the tool and the tool being arranged to deliver the stress wave caused by the impact device as a compressive stress wave to the drill bit and from there further to the rock to be drilled and the feed device being arranged to push the tool and the dril! bit against the rock to be drilled, whereby during drilling at least some of the compressive stress wave caused to the tool by the impact device is reflected as a stress wave from the rock to be drilled back to the tool.

[0002] The invention further relates to an arrangement in connection with a rock driliing rig, the rock drilling rig being provided with a rock drilling machine comprising an impact device, a feed device and a tool with a drill bit at the end thereof for breaking rock, and the impact device being arranged to cause a stress wave to the tool and the tool being arranged to deliver the stress wave caused by the impact device as a compressive stress wave to the drill bit and from there further to the rock to be drilled and the feed device being arranged to push the tool and the drill bit against the rock to be drilled, whereby during drilling at least some of the compressive stress wave caused to the tool by the impact device is reflected as a stress wave from the rock to be drilled back to the tool.

[0003] Rock drilling rigs are used for rock drilling and excavation in underground mines, quarries and excavation sites. Known rock drilling and excavation methods are cutting, crushing and percussive methods, for example. Percussive methods are most commonly used in connection with hard rock types. The percussive method involves subjecting the tool of the rock drilling machine to both rotation and percussion. However, it is the percussion that primarily breaks the rock. Rotation mostly serves to ensure that the buttons or other cutting parts of the drill bit at the distal end of the too! always hit a new spot on the rock. A rock drilling machine usually comprises a hydraulically operated impact device, whose impact piston allows the necessary compressive stress waves to be produced to the tool. Efficient breaking of rock with a per- cussive method requires that the drill bit rests against the rock at the moment of the blow. The energy associated with the impact of the impact device causes a compressive stress wave to the tool, from there further to the drill bit at the end of the tool and then to the rock. Usually in all drilling conditions some of the compressive stress wave directed to the rock is reflected back in the form of a stress wave from the rock to the tool of the rock drilling machine.

[0004] Publication WO 2006/126933 discloses a method for controlling drilling on the basis of the amount of energy in the stress wave reflected from the rock being drilled to the tool. According to the method, at least one parameter value is defined to represent the amount of the energy in the stress wave reflected from the rock. Further, the parameter value is used for adjusting the rise time and/or the duration of the stress wave generated by the pulse generator of the impact device. The parameter value also allows the amplitude of the stress wave generated by the pulse generator to be adjusted. The aim of the solution of the publication is to minimise the amount of the reflected energy and to thereby improve the efficiency of the drilling system.

[0005] One of the weaknesses of the system, however, is that the amount of the reflected stress wave energy is difficult to measure. Figure 2 shows a schematic view of a compressive stress wave entering rock during drilling and a stress wave reflected from the rock. In the reflected stress wave of Figure 2 the compressive stress reflected from the rock to be drilled back to the tool is indicated to be positive and the tensile stress negative. The amount of energy of the compressive stress wave σ_t generated by the pulse generator can be calculated with the formula

and the amount of energy of the stress wave σ,. reflected from the rock to be drilled back to the tool, in turn, can be calculated with the formula whereA is the cross-sectional surface of the tool, i.e. the drill rod, Y is an elasticity modulus, c is wave speed in the tool, ti is the duration of the compressive stress wave O₁ entering from the tool to the rock to be drilied and tr is the duration of the stress wave σ_r reflected from the rock to be drilled back to the tool. Formula (2) dearly shows that involution in the calculation of the reflected stress wave energy causes sign information of the reflected stress wave to be lost, i.e. information on which portion of the reflected stress wave energy is compressive stress and which portion tensile stress.

[0006] Moreover, the amount of the reflected energy fails to illustrate reliably the prevailing rock conditions, if the drilling suddenly enters a cavity, the compressive stress wave generated by the pulse generator of the impact device is reflected back from the rock end of the tool entirely as a reflected tensile wave. Thus the efficiency of the stress wave is of course 0%. When an extremely hard rock is being drilled, the compressive stress wave is reflected back almost entirely in the form of a compressive stress wave. Also in that case efficiency is almost 0%. in other words, in both cases the energy of the compressive stress wave is reflected back almost entirely irrespective of the fact that the drilling conditions are completely different and completely opposite adjustments are needed for the driiling.

[0007] Consequently, impact device control that would operate reliably in different drilling conditions cannot be provided on the basis of the amount of energy in the stress wave reflected from the rock to be drilled back to tool.

SUMMARY OF THE INVENTION

[0008] The object of the invention is to provide a novel solution for controlling the operation of a drilling machine.

[0009] The method of the invention is characterized by measuring at least one measurement signal representing a stress wave reflected from the rock to be drilled to the tool, determining a momentum or a parameter representing the momentum of the stress wave reflected from the rock to be drilled to the tool on the basis of the measurement signal and adjusting the operation of the impact device and/or that of the feed device on the basis of the momentum or the parameter representing the momentum of the stress wave reflected from the rock to be drilled to the tool.

[0010] The arrangement of the invention is characterized in that the arrangement further includes at least one measuring device arranged to measure at least one measurement signal representing the stress wave reflected from the rock to be drilled to the tool and that the arrangement further includes at least one control and data processing unit arranged to determine on the basis of the measurement signal of the measuring device a momentum or a parameter representing the momentum of the stress wave reflected from the rock to be drilled to the tool and the control and data processing unit being arranged to adjust the operation of the impact device and/or that of the feed device on the basis of the momentum or the parameter representing the momentum of the stress wave reflected from the rock to be drilled to the tool.

[0011] The method for controlling a rock drilling rig, which rock drilling rig is provided with a rock drilling machine comprising an impact device, a feed device and a tool with a drill bit at the end thereof for breaking rock, the impact device being arranged to cause a stress wave to the tool, the tool being arranged to deliver the stress wave caused by the impact device as a compressive stress wave to the drill bit and from there further to the rock to be drilled and the feed device being arranged to push the tool and the drill bit against the rock to be drilled, whereby during drilling at least some of the compressive stress wave caused to the tool by the impact device is reflected as a stress wave from the rock to be drilled back to the tool, comprises measuring at least one measurement signal representing the stress wave reflected from the rock to be drilled to the tool, determining a momentum or a parameter representing the momentum of the stress wave reflected from the rock to be drilled to the tool on the basis of the measurement signal and adjusting the operation of the impact device and/or that of the feed device on the basis of the momentum or the parameter representing the momentum of the stress wave reflected from the rock to be drilled to the tool.

[0012] The momentum of the stress wave reflected from the rock to be drilled back to the tool maintains information on whether the reflected stress wave represents tensile stress or compressive stress. In other words, the momentum of the reflected stress wave allows drilling conditions corresponding to a particular drilling moment to be identified at all times, thus allowing the operation of the rock drilling machine and even the rock drilling rig as a whole to be controlled or adjusted correctly on the basis of the prevailing drilling conditions without causing unnecessary strain to the drilling equipment.

[0013] According to an embodiment, when the momentum is small, the feed force of the feed device is increased. A small momentum indicates an underfeed situation, whereby increasing the feed force of the feed device allows a normal drilling situation to be obtained. [0014] According to a second embodiment, when the momentum is small, the length or duration of the stress wave caused by the impact device is increased and/or the intensity or the amplitude of the stress wave caused by the impact device is decreased. Hence, if the increase in the feed force of the feed device has not influenced the momentum of the reflected stress wave, the small momentum can be concluded to result from tensile stress caused by soft rock, which tensile stress may be reduced by decreasing the intensity or the amplitude of the stress wave caused by the impact device. As a result, the amplitude of the tensile stress wave decreases and the strain on the drilling equipment reduces. At the same time, the length or duration of the stress wave caused by the impact device may be increased, which allows to compensate for the decrease in the drilling speed caused by the decrease in the stress wave amplitude.

[0015] According to a third embodiment, when the momentum is great, the length of the stress wave caused by the impact device is decreased and the intensity of the stress wave caused by the impact device is increased. The decrease in the length of the stress wave caused by the impact device decreases the length of the compressive stress wave directed to the rock to be drilled and reflected therefrom, thus improving drilling efficiency. An increase in the intensity of the impact pulse of the impact device causes an increase in the amplitude of the compressive stress wave, thus increasing drilling penetration into the rock.

BRIEF DISCLOSURE OF THE FIGURES

[0016] Some embodiments of the invention will be discussed in greater detail with reference to the accompanying drawings, in which

Figure 1 is a schematic side view of a rock drilling rig, where the solution as described has been applied;

Figure 2 is a schematic view of a compressive stress wave entering rock to be drilled and a stress wave reflected from the rock;

Figure 3 is a schematic view of a compressive stress wave entering rock to be drilled and a corresponding stress wave reflected from the rock;

Figure 4 is a schematic view of a momentum corresponding to the stress waves of Figure 3;

Figure 5 is a schematic view of a tool displacement corresponding to Figures 3 and 4; Figure 6 is a schematic view of a second compressive stress wave entering a rock to be drilled and a corresponding stress wave reflected from the rock;

Figure 7 is a schematic view of a too! displacement corresponding to the stress waves of Figure 6.

[0017] For the sake of clarity, the embodiments of the invention shown in the Figures are simplified. Like parts are indicated with like reference numerals throughout the Figures.

DETAILED DISCLOSURE OF THE INVENTION

[0018] Figure 1 is a schematic and significantly simplified side view of a rock drilling rig 1 in which the solution of the invention may be utilized. The rock drilling rig 1 of Figure 1 is provided with a boom 2 at the end of which there is a feed beam 3 provided with a rock drilling machine 6 having an impact device 4 and a rotating device 5. The rotating device 5 transmits continuous rotating force to the tool 7, thus causing a bit 8 coupled to the tool 7 to change its position after an impact and to strike a new spot on the rock at the next impact. The impact device 4 is usually provided with an impact piston moving under the influence of pressure medium and striking an intermediate piece arranged to the upper end of the tool 7 or between the tool 7 and the impact device 4. Naturally an impact device 4 of a different structure is also possible. A stress wave directed to the tool may thus be generated a!so by a pressure pulse delivered to a pressure medium, for example, or by means based on electromagnetism, without a mechanically moving impact piston. In this context, the term impact device refers also to impact devices based on such characteristics. A proximal end of the tool 7 is connected to the rock drilling machine 6, a distal end of the tool 7 being provided with a fixed or detachable bit 8 for breaking rock. The proximal end of the tool 7 is shown schematically with a broken line in Figure 1. During drilling the bit 8 is pushed against the rock with a feed device 9. The feed device 9 is arranged to the feed beam 3, in relation to which the rock drilling machine 6 is movably arranged. The bit 8 is typically what is known as a drill bit provided with buttons 8a, although other bit structures are also possible. In driliing with sectional drill rods, also known as long hole drilling, a number of drill rods 10a to 10c depending on the depth of the hole to be drilled are attached between the drill bit 8 and the drilling machine 6, the drill rods forming the tool 7. [0019] Figure 1 shows the rock drilling rig 1 considerably smaller in relation to the structure of the rock drilling machine 6 that what it is in reality. For the sake of clarity, the rock drilling rig 1 of Figure 1 has only one boom 2, feed beam 3, rock drilling machine 6 and feed device 9, although it is obvious that a rock drilling rig is typically provided with a plurality of booms 2 having a feed beam 3, a rock drilling machine 6 and a feed device 9 arranged at the end of each. It is also obvious that the rock drilling machine 6 usually includes a flushing device to prevent the drill bit 8 from being blocked, although for the sake of clarity the flushing device is not shown in Figure 1. The drilling machine 6 may be hydrauϋcally operated, but also pneumatically or electrically operated.

[0020] The stress wave generated by the impact device 4 is delivered in the form of a compressive stress wave along the drill rods 10a to 10c towards the bit 8 at the end of the outermost drill rod 10c. When the compressive stress wave meets the bit 8, the bit 8 and its buttons 8a strike the material to be drilled, thereby causing a strong compressive stress due to which cracks are formed into the rock to be drilled. If the stress wave delivered by the impact device 4 is too strong in relation to the hardness of the rock, a problem that arises is an unnecessarily high tensile stress level that this creates to the drilling equipment. Continued drilling into soft rock at an excessive impact energy results for example in wearing of the screw joints between the drill rods 10a to 10c and/or premature damage of the drilling equipment due to fatigue.

[0021] For controlling or adjusting the operation of the rock drilling rig and the rock drilling machine in particular the momentum or a parameter representing the momentum of the stress wave σ_r reflected from the rock to be drilled to the tool is determined and the operation of the impact device 4 and/or the feed device 9 is controlled or adjusted on the basis of the momentum or the parameter representing it. The momentum P₁ Of the compressive stress wave σ_r from the tool 7 to the rock to be drilled may be calculated from the formula where A is the cross-sectional surface of the tool 7, i.e. the drill rod 10a to 10c, and ti is the duration of the compressive stress waveσ, . The momentum P₁ of the stress wave σ_r reflected from the rock back to the tool 7, in turn, may be calculated from the formula where tr is the duration of the stress wave σ_r reflected from the rock to be drilled back to the tool 7. Formula (4) clearly shows how the caicuiation of the momentum P_r of the reflected stress wave σ, maintains sign information of the reflected stress wave, i.e. information on which portion of the reflected stress wave represents compressive stress and which portion tensile stress. When the momentum P₁ is great, the reflected stress wave consists mainly of compressive reflection, and when the momentum P_r is small, tensile reflection is mostly concerned. When the momentum P₁ obtains the value zero, the stress wave σ_r reflected from the rock back to the tool 7 represents both tensile and compression in equal amounts.

[0022] As the stress wave σ_r reflected from the rock to be drilled to the tool 7, i.e. in the case of Figure 1 to one or more drill rods 10a to 10c, travels from the end of the too! 7 back to the end of the rock drilling machine 6, it causes a displacement at the end of the tool 7. if the stress wave reflected from the rock mostly contains tensile stress, the stress wave causes the end of the too! to move to the drilling direction. If the stress wave reflected from the rock mostly contains compressive stress, the stress wave causes the end of the tool to move towards the rock drilling machine. On the basis of this information the momentum of the reflected tension wave or the parameter representing it may be determined in various ways.

[0023] For example, the momentum of the reflected tension stress can be determined by measuring the displacement of the tool 7 directly from the end or middle of it, for example. To the immediate vicinity of the rock drilling machine 6 end of the tool 7 or in connection with it, for example, a measuring means 11 may be placed as schematically shown in Figure 1 to measure a measurement signal MS representing the stress wave σ, reflected from the rock to be drilled to the tool 7. Such a measuring means 11 may be an inductive distance sensor, for example, that transmits a voltage or power message representing the reflected stress wave as the measurement signal MS. The measurement signal MS measured by the measuring means 11 is transferred to the control and data processing unit 12 that determines the momentum P₁ of the stress wave σ_r or a parameter representing it, such as the displacement of the tool 7, on the basis of the measurement signal MS of the measuring means 11. As the reflected stress wave travels from the end of the tool 7 back to the end of the drilling machine, it causes a displacement of the tool. If reflected tensile stress is mainly concerned, the too! or the drill rod moves by the impact of the reflection wave to the drilling direction, if the reflection wave mostly consists of compressive stress, the drill rod moves towards the drilling machine. The extent of the displacement may be calculated from the formula

* f cp c p * Ac p ~ Ac p

where d_: is the displacement caused by the stress wave from the tool to the rock to be drilled, d_r \s the displacement caused by the reflected stress wave, v, is particle speed caused at the point of observation by the stress wave from the tool to the rock to be drilled, v, is particle speed caused by the reflected stress wave, c is the speed of the stress wave in the tool, or the drill rod, and p is the density of the tool material. The displacement d_r caused by the reflected stress wave takes into account the sign rule according to which the reflected stress wave corresponds to negative speed.

[0024] On the basis of formulae (5) and (6) it is easy to determine the momentum P_r of the reflected stress wave as a displacement of the tool. In other words, the too! displacement d, is a parameter representing the momentum of the reflected stress wave. When the measuring means 11 is arranged to measure the tool displacement from the end of the tool, also re-reflection of the stress wave from the drilling machine 6 end of the tool 7 must be taken into account.

[0025] The control and data processing unit 12 may be a separate control and data processing unit dedicated to the rock drilling machine 6 and controlling only the operation of the rock drilling machine 6, or it may be a unit controlling the operation of the rock drilling rig 1 as a whole. The operation of the control and data processing unit 12 may be based on programmabie logics, for example, but typically it is a device comprising different micro and signal processors performing different computing and control operations under the control of a software. Moreover, it is possible that the control and data processing unit 12 is composed of two or more separate but interconnected devices that each perform tasks defined for them, one device determining the momentum of the reflected stress wave, for example, whereas another one carries out the necessary control operations on the basis of the determined momentum.

[0026] It is also possible to determine the momentum P₁. of the reflected stress wave σ, in the example of Figure 1 by providing the tool 7 at the rock drilling machine 6 end with a hydraulic auxiliary device 13, shown very schematically in Figure 1 , where the displacement of the tool 7 end causes a pressure proportional to the displacement. By arranging the measuring means 11 to measure the pressure, i.e. when the measuring means 11 is of a pressure gauge or sensor type or a similar device, the pressure caused by the stress wave reflected from the rock to the hydraulic auxiliary means can be measured with the measuring means 11 and the momentum of the reflected stress wave or a parameter representing it determined on the basis thereof.

[0027] An example of another possibility for determining the momentum P_r of the reflected stress wave σ_r is to measure directly from the tool 7 the change caused to the too! 7 by the stress wave. This may be carried out for example by measuring the strain of the tool 7, for example, in which case the measuring means 11 may be a strain gauge, for example, arranged to the tool 7. However, due to the rotation of the tool 7 this kind of contact measurement may be problematic because of the cabling needed for transmitting the measurement signal MS. Alternatively, the momentum of the reflected stress wave can be determined by a contact-free measurement for example by measuring the particle speed of the tool 7 in the direction of travel of the stress wave, i.e. by measuring the speed of a particular point or part of the tool 7 in the direction of travel of the reflected stress wave. Particle velocity is directly proportional to the reflected stress wave. The measuring means 11 may be a laser, for example, that allows particle speed to be measured optically. The measuring means 11 may also be a coil, for example, that allows a change in the magnetic field caused by the stress wave to be measured in the tool 7.

[0028] The control or adjustment of the rock drilling machine 6 on the basis of the momentum P_r or a parameter representing the momentum of the stress wave σ_r reflected from the rock to be drilled may be carried out for example as follows. When the momentum is small, either underfeed is concerned or the rock to be drilled is soft, the result in both cases being a reflected stress wave corresponding to the tensile stress. In an underfeed situation the bit 8 at the end of the tool 7 or the drill bit is not resting properly against the rock during impact. Hence a gap forms between the bit 8 and the rock, causing a tensile stress wave in accordance with the free end boundary condition, in a soft rock the bit 8 substantially follows the free end boundary condition at least at the beginning of the stress pulse directed to the tool 7 and thereby to the drill bit, producing as a result also a reflected stress wave containing mostly tensile stress.

[0029] There is an extremely simple way of distinguishing between an underfeed situation and drilling of soft rock, in an underfeed situation the feeding force to be supplied to the drilling machine 6 with the feed device 9 may be increased for example by increasing the pressure in the pressure conduit 14 of the feed device 9 through adjustment of the feed pressure of the feed device pump 15 carried out by controlling the pump 15 with the control and data processing unit 12 through a control link 21. When the rock drilling machine 6 and the tool 7 and drill bit 8 associated therewith are being driven towards the rock to be drilied, pressure fluid flows in the direction of arrow A to the feed device 9. During the return motion of the feed device 9 the pressure fluid flows back to a container 17 through a return conduit 16 of the feed device 9 in the direction shown by arrow B.

[0030] If increasing the feed force has substantially no effect on the momentum, it may be concluded that a tensile stress caused by soft rock is concerned. In that case the operation of the rock drilling machine 6 may be controlled or adjusted by reducing the intensity or the amplitude of the stress wave caused by the impact device. As a result, the amplitude of the tension stress wave decreases, which reduces the strain on the drilling equipment. At the same time, the length or duration of the stress wave caused by the impact device may be increased, which allows to compensate for the decrease in the drilling speed caused by the reduced amplitude. This may be carried out for example by using the control and data processing unit 12 through a control link 20 to suitably change the pressure of the impact device 4 pump 19 located in the pressure conduit of the impact device 4 and feeding pressure fluid in the direction of arrow A' to the impact device 4. Hence the feed force of the feed device 9 may be maintained at the higher than original value or returned to its previous value. Decreasing the amplitude of the stress wave caused by the impact device 4 reduces the amplitude of the compressive stress wave directed to the rock, which naturally also reduces the amplitude of the tensile stress wave reflected from the rock, thus decreasing the momentum of the reflected stress wave. [0031] Decreasing the amplitude of the tensile stress wave protects the drilling equipment, because the tensile stresses contained in the stress wave reflected from the rock are mainly responsible for drilling equipment damages. An increase in the length of the stress wave caused by the impact device 4, in turn, compensates for the decrease in the drilling speed produced as a result of the decrease in the stress wave amplitude. When the momentum of the stress wave reflected to the tool 7 is small, it is naturally also possible to first increase the length or duration of the stress wave caused by the impact device 4 and/or to reduce the intensity or the amplitude of the stress wave before increasing the feed force of the feed device 9.

[0032] When the momentum P₁ of the stress wave σ, reflected to the tool 7 is large or great, the conclusion to be drawn is that hard rock is concerned. Hard rock causes to the tool end 7 and the bit 8 a high force opposing the penetration of the bit 8. Hence the compressive stress wave σ,from the tool

7 to the rock to be drilled does not contain sufficient power to make the drill bit

8 penetrate deeper into the rock. When the penetration of the bit 8 into the rock stops, the tool 7 end concerned obeys the fixed end boundary condition and the compressive stress wave entering the rock is reflected back to the tool 7 as a compressive stress wave. In that case the rock drilling machine 6 may be controlled or adjusted by shortening the length of the stress wave caused by the impact device 4 and by increasing the amplitude of the stress wave caused by the impact device 4, the purpose of which is to increase the penetration speed and efficiency of the drilling.

[0033] In some cases it is also possible to change the impact frequency of the impact device 4 or the drilling pulse frequency. When drilling into hard rock it is usually advantageous to increase the impact frequency. In that case the aim is not to obtain a great penetration for each impact but even a minor penetration is enough. The actual drilling speed is thus obtained by combining the small penetration of one impact with high impact frequency.

[0034] Since the momentum P, of the stress wave σ, reflected from the rock to be drilled back to the too! 7 maintains information on whether the reflected stress wave comprises tensile stress or compressive stress, it is therefore possible to correctly identify at all times the drilling conditions of a particular drilling moment on the basis of the momentum of the reflected stress wave. This enables the rock drilling machine 6 and the rock drilling rig 1 as a whole to be controlled and adjusted correctly on the basis of the prevailing driliing conditions. [0035] In the foilowing, another example of determining the momentum P₁ of stress wave σ_r reflected from the rock to be drilled, or a displacement d, of the tool 7 representing that is illustrated by way of example with reference to Figures 3 to 7. Figures 3 to 5 illustrate a case in which an extremely soft rock has been drilled, resulting in an extremely high reflected tensile stress. Figures 6 and 7, in turn, illustrate a case of drilling into an extremely hard rock. The cross-sectional surface of the drili rod used in the drilling was 1178 mm² and the material parameters of the driil rod were: stress wave velocity in the drill rod c- 5188 m/s and the drili rod material density p - 7800 kg/m³. In the Figures the compressive stress wave from the tool 7 towards the rock to be drilled is indicated by reference marking σ_s and the stress wave reflected back from the rock by reference marking σ, , as shown above. The stress wave measurement has been taken in the middle of the drill rod.

[0036] Figure 4 shows that the amount of the reflected movement was about -29.6 Ns which according to formula (6) corresponds to a displacement of about 0.6 mm to the direction of the rock to be drilled. This displacement may be confirmed from Figure 5. Figure 7, in turn, shows that the drill rod movement was about 0.48 mm to the direction of the drilling machine 6. According to formula (4) the corresponding momentum may be determined to be 23 Ns. On the basis of this it may be concluded that the reflection consisted mainly of compressive stress and that drilling into an extremely hard rock was concerned.

[0037] In some cases features disclosed in this application may be used as such, irrespective of other features. On the other hand, the features disclosed in this application may be combined to produce different combinations.

[0038] The drawings and the related specification are only meant to illustrate the inventive idea. The details of the invention may vary within the scope of the claims.

Claims

1. A method for controlling a rock drilling rig (1), the rock drilling rig (1) being provided with a rock drilling machine (6) comprising an impact device (4), a feed device (9) and a tool (7) with a drill bit (8) at the end thereof for breaking rock, and the impact device (4) being arranged to cause a stress wave to the tool (7) and the tool (7) being arranged to deliver the stress wave caused by the impact device (4) as a compressive stress wave (σ,) to the drill bit (8) and from there further to the rock to be drilled and the feed device (9) being arranged to push the tool (7) and the drill bit (8) against the rock to be drilled, whereby during drilling at least some of the compressive stress wave (σj caused to the tool (7) by the impact device (4) is reflected as a stress wave { σ_r ) from the rock to be drilled back to the tool (7) , characterized by measuring at least one measurement signal (MS) representing a stress wave (σ, ) reflected from the rock to be drilled to the tool (7), determining a momentum (P₁) of the stress wave (σ,) reflected from the rock to be drilled to the tool (7) or a parameter representing the momentum on the basis of the measurement signal and adjusting the operation of the impact device (4) and/or that of the feed device (9) on the basis of the momentum {P_r ) or the parameter representing the momentum of the stress wave (σ_r) reflected from the rock to be drilled to the tool (7).

2. A method according to claim ^ characterized by measuring a displacement (D) of the tool (7) and determining on the basis of the displacement (D) of the tool (7) the momentum (P, ) of the stress wave (σ, ) reflected from the rock to be drilled to the tool (7).

3. A method according to claim 1 or 2, c h a r a c t e r i z e d by arranging a hydraulic auxiliary device (13) to the tool (7) and measuring the pressure acting on the hydrauiic auxiliary device (13) and determining on the basis of the pressure the momentum (P₁) of the stress wave (σ_r) reflected from the rock to be drilled to the tool (7) or a parameter representing the momentum, such as the displacement (D) of the too! (7).

4. A method according to any one of the preceding claims, characterized by measuring directly from the tool (7) the change caused to the too! (7) by the reflected stress wave (σ_r ).

5. A method according to any one of the preceding claims, ch a racterized by measuring the elongation of the too! (7),

6. A method according to claim 4, ch a racte rized by measuring the particle speed of the tool (7) optically.

7. A method according to claim 4, ch aracterized by measur^¬ ing the particle speed of the tool (7) on the basis of the change in the magnetic field of the tool (7) caused by the reflected stress wave (σ_r).

8. A method according to any one of the preceding claims, ch a ra cterized in that when the momentum (P-) is small, the feed force of the feed device (9) is increased.

9. A method according to any one of the preceding claims, cha ra cte rized in that when the momentum { P_r ) is small, the length or duration of the stress wave caused by the impact device (4) is increased and/or the in^¬ tensity or the amplitude of the stress wave caused by the impact device (4) is decreased.

10. A method according to anyone of claims 1 to 7, ch a racte rize d in that when the momentum (P, ) is great, the length of the stress wave caused by the impact device (4) is decreased and the amplitude of the stress wave caused by the impact device (4) is increased.

11. A method according to any one of the preceding claims, ch a ra cterized by changing the impact frequency of the impact device (4).

12. An arrangement in connection with a rock drilling rig (1), the rock drilling rig (1) being provided with a rock drilling machine (6) comprising an impact device (4), a feed device (9) and a tool (7) with a drill bit (8) at the end thereof for breaking rock, and the impact device (4) being arranged to cause a stress wave to the tool (7) and the tool (7) being arranged to deliver the stress wave caused by the impact device (4) as a compressive stress wave (σ,) to the drill bit (8) and further to the rock to be drilled and the feed device (9) being arranged to push the tool (7) and the driii bit (8) against the rock to be drilled, whereby during drilling at least some of the compressive stress wave (σ, ) caused to the tool (7) by the impact device (4) is reflected as a stress wave ( σ_r ) from the rock to be drilled back to the tool (7), ch a ra cte rized in that the arrangement further includes at least one measuring device (11) arranged to measure at least one measurement signal (MS) representing the stress wave (σ_r ) reflected from the rock to be drilled to the tool (7) and that the arrangement further includes at least one control and data processing unit (12) arranged to determine on the basis of the measurement signal of the measuring device (11) a momentum (P₁ ) or a parameter representing the momentum of the stress wave (σ_r) reflected from the rock to be drilled to the tool (7) and the control and data processing unit (12) being arranged to adjust the operation of the impact device (4) and/or that of the feed device (9) on the basis of the momentum (P, ) or the parameter representing the momentum of the stress wave (σ_r ) reflected from the rock to be drilled to the tool (7).

13. An arrangement according to claim 12, characterized in that the measuring means (11) is arranged to measure the displacement (D) of the tool (7).

14. An arrangement according to claim 12, characterized in that the arrangement further includes a hydraulic auxiliary device (13) arranged to the tool (7) and that the measuring means (11) is arranged to measure the pressure acting on the hydraulic auxiliary device (13).

15. An arrangement according to claim 12, characterized in that the measuring means (11 ) is arranged to measure directly from the tool (7) the change caused to the tool (7) by the reflected stress wave (σ, ).

16. An arrangement according to claim 15, characterized in that the measuring means (11) is arranged to measure the elongation of the tool (7).

17. An arrangement according to claim 15, characterized in that the measuring means (11) is arranged to measure the particle speed of the too! (7) optically.

18. An arrangement according to claim 15, characterized in that the measuring means (11) is arranged to measure the particle speed of the tool (7) on the basis of the change in the magnetic field of the tool (7) caused by the reflected stress wave (σ_r ).

19. An arrangement according to any one of claims 12 to 18, characterized in that when the momentum is small, the control and data processing unit (12) is arranged to control the operation of the feed device (9) so that the feed force of the feed device (9) is increased.

20. An arrangement according to any one of claims 12 to 19, c h a r - a c t e r i z e d in that when the momentum is small, the control and data processing unit (12) is arranged to control the operation of the impact device (4) so that the length or duration of the stress wave caused by the impact device (4) is increased and/or the intensity or the amplitude of the stress wave caused by the impact device (4) is decreased.

21. An arrangement according to any one of claims 12 to 18, characterized in that when the momentum ( P_r ) is great, the control and data processing unit (12) is arranged to shorten the length of the stress wave caused by the impact device (4) and to increase the amplitude of the stress wave caused by the impact device (4).

22. An arrangement according to any one of claims 12 to 21, characterized in that control and data processing unit (12) is arranged to change the impact frequency of the impact device (4).