Rock Quality Judgment Device and Drilling Machine

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of foreign priority to Japanese Patent Application Nos. JP2024-147394, filed Aug. 29, 2024, and JP2025-101630, filed Jun. 17, 2025, each of which is incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a rock quality judgment device mounted on a drilling machine and the drilling machine.

BACKGROUND

In a blasting method in which a blast hole is drilled into bedrock using a drilling machine, grasping a state of the bedrock enables blasting work to be performed safely and efficiently.

As an example of a method for grasping rock quality, advanced prediction is generally performed when a tunnel is drilled with a drill jumbo (See, e.g., Patent Publication No. JP 2015-067957 A).

Although, in tunnel drilling, a drilling route is determined after performing boring survey from the ground surface in advance, JP 2015-067957 A describes that utilizing a rock classification obtained from the boring survey as reference data enables a more precise advanced prediction to be performed.

SUMMARY

However, differing from tunnels that are maintained as social infrastructure, in an open-pit mine or quarry, boring survey across the whole area of the mining site is not performed. Therefore, when a crawler drill is used to drill blast holes in an open-pit mine or quarry, it is difficult to employ the technology described in JP 2015-067957 A.

In addition, the technology described in JP 2015-067957 A is a technology of advanced prediction performed under predetermined conditions before face drilling, and is not a technology for performing rock quality judgment in a blast hole drilled in an actual operation.

In addition, in a mine or the like, performing blasting while explosive is appropriately charged in accordance with rock quality leads to improvements in production efficiency and safety. That is, it becomes easier to crush rock in a planned crushing granularity, and it becomes possible to control the amount of scattering of flying stones.

The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to, by drilling a blast hole using a crawler drill, judge rock quality around the blast hole at the same time.

A first implementation of the invention is a rock quality judgment device configured to judge rock quality at a location at which a drilling machine including a rock drill and a feed mechanism causing the rock drill to advance is drilling. The rock quality judgment device includes a pressure acquisition unit configured to acquire actual feed pressure, the actual feed pressure being feed pressure being actually supplied to the feed mechanism, a command pressure acquisition unit configured to acquire feed command pressure, the feed command pressure being a command value of the feed pressure, and a rock quality judgment unit configured to judge rock quality based on a value acquired by the pressure acquisition unit and a value acquired by the command pressure acquisition unit. The rock quality judgment unit judges the rock quality as stable rock when the actual feed pressure is greater than or equal to the feed command pressure and judges the rock quality as unstable rock when the actual feed pressure is less than the feed command pressure.

A second implementation of the invention is the rock quality judgment device according to the first implementation that further includes a criterion storage unit configured to set a plurality of numerical value ranges for a value taken by a differential pressure value, the differential pressure value being a difference between the actual feed pressure and the feed command pressure, and to store the plurality of numerical value ranges. The criterion storage unit stores each of the plurality of numerical value ranges in association with one of types of rock quality classified as stable rock. When judging the rock quality as the stable rock, the rock quality judgment unit further calculates the differential pressure value and judges the rock quality as a type of rock quality corresponding to a numerical value range in which the differential pressure value is included.

A third implementation of the invention is the rock quality judgment device according to the second implementation where the criterion storage unit further stores an additional judgment range as the numerical value range between numerical value ranges corresponding to types of rock quality classified as the stable rock. The rock quality judgment unit determines, when the differential pressure value is included in one of the numerical value ranges each corresponding to one of the types of rock quality, a corresponding type of rock quality as a judgment result, and further performs, when the differential pressure value is included in the additional judgment range, an additional judgment. The additional judgment is a rock quality judgment processing not based on the differential pressure value and determines a judgment result of the additional judgment as a final judgment result.

A fourth implementation of the invention is the rock quality judgment device according to the third implementation where the criterion storage unit stores at least a numerical value range corresponding to hard rock, a numerical value range corresponding to medium-hard rock, a numerical value range corresponding to soft rock, a first additional judgment range, the first additional judgment range being a numerical value range between the hard rock and the medium-hard rock, and a second additional judgment range. The second additional judgment range is a numerical value range between the medium-hard rock and the soft rock.

A fifth implementation of the invention is the rock quality judgment device according to the third implementation that further includes a drilling speed acquisition unit configured to acquire drilling speed, and a hammering pressure acquisition unit configured to acquire hammering pressure of the rock drill. The criterion storage unit stores a relationship among hammering pressure, the actual feed pressure, and drilling speed corresponding to a type of rock quality classified into the stable rock, and the rock quality judgment unit performs rock quality judgment based on the hammering pressure, drilling speed, and the actual feed pressure as the additional judgment.

A sixth implementation of the invention is a drilling machine that includes the rock quality judgment device according to any one of the first to fifth implementations.

According to implementations of the present invention, it is possible to, by drilling a blast hole using a crawler drill, judge rock quality around the blast hole at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrative of a structure of a drilling machine according to implementations of the present invention and blast holes.

FIG. 2 is a hydraulic circuit diagram of the drilling machine according to implementations of the present invention.

FIG. 3 is a block diagram illustrative of a configuration of a rock quality judgment device according to implementations of the present invention.

FIG. 4 is a diagram illustrative of a rock quality judgement flow.

FIG. 5 is a diagram graphically illustrative of a judgment criterion that the drilling machine according to implementations of the present invention stores in a criterion storage unit.

FIG. 6 is a diagram illustrative of another rock quality judgement flow.

FIGS. 7A and 7B are, respectively, a rock quality map at the time of high hammering pressure setting and a rock quality map at the time of low hammering pressure setting that the drilling machine according to implementations of the present invention stores in the criterion storage unit.

DETAILED DESCRIPTION

Embodiments of the present invention will be described with reference to the drawings as appropriate. Note that the drawings to be referred to are schematic. Therefore, it should be noted that relations between thicknesses and planar dimensions, ratios, and the like are different from actual ones and portions having different dimensional relationships and ratios from one another among the drawings are included.

In addition, the following embodiments indicate devices and methods to embody the technical idea of the present invention by way of example, and the technical idea of the present invention does not limit the materials, shapes, structures, arrangements, and the like of the constituent components to those described below.

As a definition of terms, unless specifically specified, term “pressure”, such as “feed pressure”, is used as a word meaning pressure of hydraulic oil, such as operating pressure of corresponding hydraulic equipment, in the following description.

In addition, “feed command pressure” and “actual feed pressure”, which are terms used in the description, are illustrated in the drawings as “command pressure” and “actual pressure” in an abbreviated manner.

Structure of Drilling Machine

A structure of a drilling machine will be described with reference to FIG. 1.

A drilling machine 1 includes a traveling carriage 2 and a guide shell 7. The traveling carriage 2 includes a carriage body 3, a truck frame 4, and an operator cabin 5.

In the carriage body 3, an engine (illustration is omitted) that is a power source of the drilling machine 1, a flushing mechanism 18 that is hydraulic/pneumatic equipment, a dust collector 19, a hydraulic pump Pp (FIG. 2), other various types of hydraulic/pneumatic equipment, and a control device 20 that controls the foregoing hydraulic/pneumatic equipment are installed. Details of the hydraulic/pneumatic equipment will be described later.

A boom 6, the rear end portion of which is supported by the traveling carriage and to the front end portion of which the guide shell 7 is connected, is installed at a front portion of the traveling carriage 2. The boom 6 supports the guide shell 7 in such a manner that a posture thereof is changeable within a predetermined range.

In the guide shell 7, a rock drill 8 is provided in an advanceable and retractable manner by a feed mechanism 11 that generates thrust force in a drilling direction. That is, the feed mechanism causes the rock drill to advance.

A rod 12 is attached to the rock drill 8, and a bit 13 for drilling is attached to a tip of the rod 12. Note that the bit 13 is a component fixed to the tip of the rod 12 to crush bedrock, and the bit 13 is installed only to the rod 12 located at the head position.

On the lateral side of the guide shell 7, a rod changer 14 and a rod magazine 15 are provided.

A plurality of extension rods 12b without a bit 13 are loaded in the rod magazine 15. At the time of installation of an extension rod 12b, the rod changer 14 picks up the extension rod 12b from the rod magazine 15 and moves the extension rod 12b to a connection position to the rock drill 8.

The rock drill 8 includes a hammering mechanism 9 that generates hammering power and a rotation mechanism 10 that generates rotational force. In addition, an opening/closing type centralizer 16 is provided at a tip portion of the guide shell 7, and a suction cap 17 is provided in an advanceable and retractable manner along the drilling direction.

Setting of the hammering mechanism 9 is selectable between a high hammering pressure setting that is used at the time of main drilling and a low hammering pressure setting that is used at the time of collaring stage of drilling. When being set to the low hammering pressure setting, the hammering mechanism 9 strikes a blow with a lower hammering pressure than when being set to the high striking pressure setting. As shown, change between the high and low hammering pressure settings is performed by operating a hammering pressure change lever (illustration is omitted) provided inside the operator cabin 5.

The centralizer 16 supports the rod 12 on the tip end side of the guide shell 7 and maintains an axial direction of the rod 12 in alignment with the feeding direction of the rock drill 8.

The suction cap 17 covers an opening of a blast hole BH during drilling operation and prevents discharged cuttings from scattering to surroundings. In addition, piping to the dust collector 19 is connected to the suction cap 17.

The dust collector 19 sucks and collects the cuttings from the suction cap 17 through the piping and discharges the collected cuttings from a rear portion of a machine body.

The flushing mechanism 18 includes a series of devices that feeds compressed air supplied from a compressor (illustration is omitted) to the bit 13 and blows out the compressed air into the blast hole BH being drilled and thereby generates an air flow for exhausting the cuttings to the outside of the blast hole BH.

Configuration of Rock Quality Judgment Device

A rock quality judgment device 50 will be described with reference to FIGS. 2 and 3.

Note that a hydraulic circuit diagram illustrated in FIG. 2 illustrates only elements associated with the present disclosure in a circuit from the hydraulic pump Pp to a feed motor 11a via a feed pressure adjustment valve 31 and a differential pressure reducing valve 32. Illustration of elements not directly related to the present disclosure may be omitted.

Hydraulic Circuit Configuration of Drilling Machine

As illustrated in FIG. 2, the drilling machine 1 includes, in a hydraulic circuit between the hydraulic pump Pp and the feed motor 11a, the feed pressure adjustment valve 31, the differential pressure reducing valve 32, and a feed advance speed adjustment valve 33.

Note that although illustration is omitted, a main valve that is a control valve to supply hydraulic oil in a distributed manner to the respective hydraulic equipment included in the drilling machine 1 is provided between the hydraulic pump Pp and the differential pressure reducing valve 32.

The feed pressure adjustment valve 31 is connected to a pilot passage (a part indicated by a dashed line in FIG. 2) of the differential pressure reducing valve 32 to adjust feed command pressure. Note that the feed pressure adjustment valve 31 may be installed in the operator cabin 5 (FIG. 1) for operation by the operator or may be controlled by the control device 20 (FIG. 1) regardless of installation position.

The differential pressure reducing valve 32 is a device that is installed between the main valve and the feed advance speed adjustment valve 33 and that adjusts the amount of hydraulic oil supplied to the feed motor 11a based on feed command pressure set by the feed pressure adjustment valve 31.

The feed advance speed adjustment valve 33 is installed between the differential pressure reducing valve 32 and the feed motor 11a and defines the amount of hydraulic oil supplied to the feed motor 11a.

Tanks T are installed on the downstream sides of the feed pressure adjustment valve 31 and the feed motor 11a.

The differential pressure reducing valve 32 is a device that reduces pressure from the pump (primary pressure) to reduced pressure (secondary pressure) according to pressure set by the feed pressure adjustment valve 31 (feed command pressure). The differential pressure reducing valve 32 includes a spring and a spool and has a structure in which the spool stops when force generated by the secondary pressure is balanced with the combined force generated by the feed command pressure and the spring. That is, when a sufficiently large load is applied to the feed motor 11a, the secondary pressure becomes greater than (or at least equal to) the feed command pressure by an amount equivalent to the force generated by the spring.

A plurality of sensors to acquire numerical values to be used for rock quality judgment are installed in the hydraulic circuit between the hydraulic pump Pp and the feed motor 11a.

In the pilot passage from the differential pressure reducing valve 32, a feed command pressure sensor 51 is installed between the feed pressure adjustment valve 31 and the differential pressure reducing valve 32.

In addition, a gauge PG for the operator to confirm command operating pressure is also connected between the feed pressure adjustment valve 31 and the differential pressure reducing valve 32. The gauge PG is installed inside the operator cabin 5 illustrated in FIG. 1.

An actual feed pressure sensor 52 is installed between the feed advance speed adjustment valve 33 and the feed motor 11a.

The feed command pressure sensor 51 is a command pressure acquisition unit that acquires the feed command pressure that is a command value of the feed pressure.

The actual feed pressure sensor 52 is a pressure acquisition unit that acquires actual feed pressure that is feed pressure actually supplied to the feed motor 11a.

Note that the drilling machine 1 may have a configuration that includes the differential pressure reducing valve 32 on the downstream side of the feed advance speed adjustment valve 33 and that includes the feed motor 11a and the actual feed pressure sensor 52 on the downstream side of the differential pressure reducing valve 32, that is, a configuration in which the positions of the differential pressure reducing valve 32 (including the feed pressure adjustment valve 31 and the pilot passage) and the feed advance speed adjustment valve 33 in FIG. 2 are replaced with each other.

Rock Quality Judgment Device

A configuration of the rock quality judgment device 50 will be described with reference to FIG. 3.

The rock quality judgment device 50 includes, in addition to the feed command pressure sensor 51 and the actual feed pressure sensor 52 that are described above as sensors, a hammering pressure sensor 53 (or hammering pressure acquisition unit) and further includes a drilling speed calculation unit 54 (or drilling speed acquisition unit), a criterion storage unit 55, a rock quality judgment unit 56, and a rock quality storage unit 57.

Among the above-described constituent components, only the rock quality storage unit 57 is connected to the output side of the rock quality judgment unit 56, while the other constituent components are connected to the input side of the rock quality judgment unit 56.

The feed command pressure sensor 51 and the actual feed pressure sensor 52 are pressure sensors that acquire feed command pressure and actual feed pressure, respectively, as described in the hydraulic circuit configuration.

The hammering pressure sensor 53 is a pressure sensor installed in the hydraulic circuit of the hammering mechanism 9 and acquires the hammering pressure that is operating pressure of the hammering mechanism.

The drilling speed calculation unit 54 is connected to the feed motor 11a and calculates advancing speed of the rock drill 8.

The criterion storage unit 55, although details will be described later, stores information that is referred to in rock quality judgment processing.

The rock quality judgment unit 56 performs rock quality judgment processing based on acquired and calculated information and a criterion value.

The rock quality storage unit 57 stores a judgment result of the rock quality judgment unit in association with location information and drilling depth information of a blast hole BH.

Rock Quality Judgment Processing

Overview

Details of the rock quality judgment processing will be described mainly with reference to FIGS. 4 to 7.

In the present embodiment, the judgment is basically performed using a differential pressure value between the actual feed pressure and the feed command pressure (hereinafter, referred to as “differential pressure value judgment”). When rock quality is judged as stable rock, and the differential pressure value is a numerical value within a predetermined range, judgment using a relationship between the actual feed pressure and drilling speed (hereinafter, referred to as an “additional judgment”) is performed.

Classification of Stable Rock and Unstable Rock

Unstable rock to be judged in the present disclosure is a type of rock that has a tendency that working pressure of the feed motor 11a is unlikely to increase, and a clay layer, a fracture zone, and a cavity correspond to unstable rock. On the other hand, stable rock is a type of rock that is stable and tends to stabilize while the working pressure of the feed motor 11a is high, and soft rock, medium-hard rock, and hard rock correspond to stable rock.

Note that distinction among hard rock, medium-hard rock, and soft rock defined in the present embodiment is a result of arbitrarily settable relative evaluation. For example, it is possible to set a rock quality that is judged as hard rock at a site A to be judged as soft rock at a site B. As described above, in the present embodiment, a criterion for rock quality evaluation is set at each site where the drilling machine 1 is operated. Therefore, a criterion, such as a numerical value range, illustrated and described below merely indicates an example.

Differential Pressure Value Judgment

The differential pressure value judgment is performed by comparing the actual feed pressure of the feed motor 11a with the feed command pressure.

As illustrated in FIG. 4, the rock quality judgment unit 56 judges, when the actual feed pressure of the feed motor 11a while the drilling is performed (S01: YES) is lower than the feed command pressure (S02: YES), the rock quality as unstable rock (S03) and judges, when the actual feed pressure of the feed motor 11a is higher than the feed command pressure (S02: NO), the rock quality as stable rock (S04). That is, in the differential pressure value judgment, the rock quality judgment unit 56 judges the rock quality, based on a value acquired by the pressure acquisition unit and a value acquired by the command pressure acquisition unit.

Note that in the present embodiment, a predetermined drilling depth is used as a minimum unit of judgment. Specifically, judgment is made by acquiring values of the actual feed pressure and values of the feed command pressure at a constant sampling interval while the feed motor 11a rotates by a predetermined angle and comparing arithmetic averages of the acquired values.

Although the secondary pressure of the differential pressure reducing valve 32 reaches the feed motor 11a via hydraulic piping and the feed advance speed adjustment valve 33, pressure loss according to a flow rate occurs on this occasion.

Generally, because devices that incur only slight pressure loss when drilling stable rock are selected as the hydraulic piping and the feed advance speed adjustment valve 33, “actual feed pressure≥feed command pressure” holds.

On the other hand, drilling speed and a feed flow rate increase when drilling unstable rock, and a large pressure loss occurs. Therefore, “actual feed pressure<feed command pressure” holds.

When after the judgment of stable rock, the rock quality is further classified, the judgment is also made using the feed command pressure and the actual feed pressure of the feed motor 11a (S05).

FIG. 5 is a diagram graphically illustrative of information that the criterion storage unit 55 refers to in the “differential pressure value judgment”.

Specifically, the criterion storage unit 55 sets a plurality of numerical value ranges for a value taken by the differential pressure value, which is a difference between the actual feed pressure and the feed command pressure, and stores each of the numerical value ranges in association with one of types of rock quality that are classified as stable rock. Further, a numerical value range between the numerical value ranges corresponding to the types of rock quality classified as stable rock is stored as an additional judgment range.

The plurality of numerical value ranges, each of which corresponds to a type of rock quality, may be a respective numerical value range corresponding to hard rock H, a numerical value range corresponding to medium-hard rock MH, and a numerical value range corresponding to soft rock S.

FIG. 5 is drawn in such a manner that a point at which the differential pressure value is 0 (actual feed pressure=feed command pressure) is set as the origin, and the differential pressure value increases toward the right-hand side (actual feed pressure>feed command pressure). The numerical value ranges correspond to the soft rock S, the medium-hard rock MH, and the hard rock H in ascending order of the differential pressure value.

In addition, the criterion storage unit 55 stores at least a numerical value range between the hard rock H and the medium-hard rock MH as a first additional judgment range AJ1 and a numerical value range between the medium-hard rock MH and the soft rock S as a second additional judgment range AJ2.

As illustrated in FIG. 4, when the differential pressure value is a numerical value falling within a numerical value range that corresponds to one of the types of rock quality, the rock quality judgment unit 56 determines the corresponding type of rock quality as a judgment result (S06 to S08). The judgment result is stored in the rock quality storage unit in association with information about the location and drilling depth of the blast hole BH (S09).

When the differential pressure value is a numerical value falling within the first additional judgment range AJ1 or the second additional judgment range AJ2, the rock quality is judged by additional judgment processing (S10) described below.

Additional Judgment Processing

As illustrated in FIG. 6, the additional judgment processing is a rock quality judgment system that is performed based on the hammering pressure, the actual feed pressure, and the drilling speed and that does not use the differential pressure value. The additional judgment processing is a judgment system that is particularly suitable for judgment of stable rock.

In the additional judgment, first, calculation of drilling speed is performed based on the amount of feed per unit time (S11), and next or simultaneously, acquisition of actual feed pressure (S12) and acquisition of hammering pressure (S13) are performed.

The criterion storage unit 55 stores rock quality maps illustrated in FIGS. 7A and 7B, where the numerical value range corresponding to the soft rock S, the numerical value range corresponding to the medium-hard rock MH, and the numerical value range corresponding to the hard rock H are set according to a combination of the drilling speed and the actual feed pressure. The rock quality maps are a compilation of information about a relationship between the drilling speed corresponding to the feed pressure and rock hardness.

In FIGS. 7A and 7B, it is meant that with the lower left corner as the origin, the further toward the right-hand side, the faster the drilling speed is, and the further toward the upper side, the higher the actual feed pressure is. That is, it is visualized that when operated with a certain feed pressure, the slower the drilling speed is, the harder the rock is, and the higher the actual feed pressure required to exert a certain drilling speed is, the harder the rock is.

Because the magnitude of hammering pressure is related to the amount of energy input during drilling, a location at which the rock quality is judged as the hard rock H differs between the graph in FIG. 7A when high hammering pressure is provided and the graph in FIG. 7B when limited hammering pressure is provided. Specifically, in the graph in FIG. 7B indicating the rock quality map at the time of the low hammering pressure setting, the numerical value ranges indicating the types of rock quality are shifted to the right-hand side compared with the graph in FIG. 7A. In other words, FIG. 7B illustrates judgment criteria when the drilling speed becomes slow due to a reduction in hammering pressure.

The rock quality maps that are referred to at the time of rock quality judgment based on the additional judgment need to provide different judgment results depending on the hammering pressure at the time of drilling. Therefore, the rock quality maps are switched based on the acquired hammering pressure before the rock quality judgment processing is performed (S14).

In the present embodiment, the rock quality map at the time of the high hammering pressure setting illustrated in FIG. 7A and the rock quality map at the time of the low hammering pressure setting illustrated in FIG. 7B are switched. This is a correction method for the rock quality map under the assumption that the drilling machine 1 having a configuration in which the operator, without setting the hammering pressure in detail, performs only a simple operation such as switching preset hammering modes is used. Therefore, it may be configured such that a formula for correction is stored in the criterion storage unit 55 and the correction of the rock quality map is performed each time.

As illustrated in FIG. 6, after switching of the rock quality map (or adjusting values according to the formula for correction), the rock quality judgment unit 56 performs rock quality judgment using the drilling speed and the actual feed pressure with reference to the rock quality map (S15 to S18).

Then, a judgment result in the additional judgment processing is stored as a final judgment result in association with the information about the drilling depth in the rock quality storage unit 57 (S09 in FIG. 4).

By repeating the above-described judgment processing, rock quality information of a whole area in the blast hole BH is recorded.

Advantageous Effects

In embodiments of the present invention, by drilling a blast hole using a crawler drill, it is possible to judge rock quality around the blast hole at the same time. Therefore, there is no need to perform test drilling or examination after drilling, and it is possible to record information relating to rock quality while drilling a blast hole.

In addition, embodiments of the present invention distinguish stable rock and unstable rock as a largest unit of classification. In particular, unstable rock is likely to become not only a factor for posing a problem for explosive charging operation but also a factor for excessive explosive charging. Therefore, identifying a location of unstable rock in advance enables an advantageous effect in the explosive charging operation to be achieved, such as making it easier to make an appropriate explosive charging plan and enabling a process of explosive charging operation to be examined in advance.

In addition, by classifying stable rock in detail based on hardness of the rock, creation of an appropriate explosive charging plan is facilitated.

Note that although it is possible to discriminate between unstable rock and stable rock solely based on the drilling speed, accuracy of the judgment deteriorates. This is because, in actual drilling operation, the operator of drilling machine 1 sometimes intentionally reduces the feed speed, the feed pressure, and the hammering pressure to decrease the drilling speed to avoid jamming, hole bending, or the like. That is, when rock quality is always judged solely based on the drilling speed, parameters fluctuate regardless of the rock quality, the accuracy of the judgment also deteriorates.

Embodiments of the present invention are capable of performing more accurate judgment than a system in which rock quality is discriminated solely based on the drilling speed because the present invention performs the judgment using the differential pressure value between the actual feed pressure and the feed command pressure, which is less susceptible to influence of operation by the operator.

As described in the embodiments, by setting an additional judgment range between the numerical value ranges and performing the additional judgment processing, it is possible to improve the accuracy of the judgment. That is, at a site where the differential pressure value frequently oscillates across a threshold value by which the rock quality is judged as either of types of rock quality adjacent to each other, it is possible to prevent the judgment result from changing in a short period.

Variation

Although the rock quality judgment device that uses the differential pressure value judgment and the additional judgment in combination has been described above, because the disclosure relies in comparing the differential pressure between the actual feed pressure and the feed command pressure for driving the feed motor 11a and judging stable rock and unstable rock, setting of an additional judgment range and employment of the additional judgment can be arbitrarily determined. In addition, it may be configured such that only judgment of stable rock and unstable rock is performed.

The following is a list of reference signs used in this specification and in the drawings.

• • 1 Drilling machine
  • 8 Rock drill
  • 9 Hammering mechanism
  • 10 Rotation mechanism
  • 11 Feed mechanism
  • 11a Feed motor
  • 20 Control device
  • 31 Feed pressure adjustment valve
  • 32 Differential pressure reducing valve
  • 33 Feed advance speed adjustment valve
  • 50 Rock quality judgment device
  • 51 Feed command pressure sensor
  • 52 Actual feed pressure sensor
  • 53 Hammering pressure sensor
  • 54 Drilling speed calculation unit
  • 55 Criterion storage unit
  • 56 Rock quality judgment unit
  • 57 Rock quality storage unit
  • H Hard rock
  • MH Medium-hard rock
  • S Soft rock
  • AJ1 First additional judgment range
  • AJ2 Second additional judgment range